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It is now 18 years since tabletop laser wakefield accelerators (LWFAs) generated "dream beams" of MeV electrons with 10% energy spread [1]. Yet despite scaling of energy gain to the multi-GeV level [2], generation of e-bunches with sub-% energy spreads needed for major applications, design of LWFAs for positrons needed for colliders, and high-resolution diagnosis of LWFA structures and e-beams needed for reliable operation remain outstanding challenges for the field.  I will discuss our recent simulations [2,3] and experiments [4-7] aimed at addressing these unsolved problems. 

[1] S. P. D. Mangles, Nature431, 535 (2004); C. G. R. Geddes et al., Nature431, 538 (2004); J. Faure et al., Nature431, 541 (2004).

[2] A. J. Gonsalves et al., "Petawatt laser guiding and electron beam acceleration to 8 GeV in a laser-heated capillary discharge waveguide," Phys. Rev. Lett. 122, 084801 (2019).

[3] P. Kumar et al., "Evolution of self-injection process in long wavelength infrared laser driven LWFA," Phys. Plasmas28, 013102 (2021).

[4] T. Silva et al., "Stable positron acceleration in thin, warm, hollow plasma channels," Phys. Rev. Lett. 127, 104801 (2021).

[5] R. Zgadzaj et al., "Dissipation of electron-beam-driven plasma wakes," Nature Commun. 11, 4753 (2020).

[6] Y. Chang et al., "Faraday rotation study of plasma bubbles in GeV wakefield accelerators," Phys. Plasmas 28, 123105 (2021),

[7] A. H. Lumpkin et al., "Coherent optical signatures of electron microbunching in laser-driven plasma accelerators," Phys. Rev. Lett. 125, 014801 (2020).

Over the past five years the number of fusion energy startup companies has doubled and private funding going to fusion companies has grown by a much larger factor. This talk will provide an overview of the fusion energy startup landscape focusing on their funding, technology, progress, and future plans.

Physicists and engineers frequently encounter situations in which there is a need to evaluate and optimize via numerical simulation the performance of a particular device or system.  This leads to calculating a figure of merit (FoM) characterizing the system and its gradient in a high dimensional parameter space.  Direct evaluation of the gradient via finite differencing each parameter can become computationally expensive when there are many parameters. In this case a computational savings can be achieved if an “adjoint problem” can be found that produces the desired information without requiring multiple computations. A simple example is the design of a receiving antenna. One wishes to know and optimize the signal received as a function of the incident angle and polarization of incoming waves. It might appear that solution of Maxwell’s field equations would have to be repeated for each possible incident direction and polarization. However, due to the reciprocal property of the governing equations, the desired information is obtained by treating the antenna as a transmitter and calculating the far field radiation pattern. Thus, one computation replaces many. In this talk I will review some problems from the area of plasma physics and charged particle dynamics where adjoint methods have proven useful. Examples include calculation of the plasma current driven by absorption of RF waves in magnetic confinement fusion devices, determination of the sensitivity of stellarator equilibria to changes in magnetic coil locations, optimization of electron beam optics in diodes and accelerator lattices, and optimization of slow wave structures used in microwave and millimeter wave amplifiers.

General relativistic magnetohydrodynamics (GRMHD) modeling is a powerful tool for describing the extreme plasma dynamics around compact objects including black holes. In such systems, the infalling plasma forms an accretion disk, which releases energy in the form of radiation, winds and Poynting-flux dominated jets. While GRMHD simulations have been successful in describing the large-scale plasma dynamics around slowly accreting black holes, the spatial scales on which dissipative processes are expected to converge were not resolved, which led to significant uncertainties in our understanding of non-thermal emission processes. On the other hand, the plasma around rapidly accreting black holes rapidly cools and collapses into a razor-thin disk, which is hard to resolve numerically and has presented an unsolved challenge for 3D GRMHD modeling. To tackle these and other challenging problems, I have developed the first graphics processing unit (GPU) accelerated radiative GRMHD code H-AMR and deployed it on the nation's largest supercomputer OLCF Summit. In the first part of my talk, I will discuss a wide range of algorithmic optimizations I have implemented in H-AMR to achieve excellent performance on a single GPU. I will then describe the load balancing routines and techniques I have developed to attain scalability (up to 6000 GPUs) on world's largest GPU clusters. In the second part of my talk I will highlight several groundbreaking discoveries enabled by global 3D GRMHD simulations with H-AMR: (i) self-consistent formation of multi-phase corona-like plasma in the presence of large scale magnetic flux, (ii) 3D plasmoid-mediated reconnection, and (iii) shredding of accretion disks by the frame dragging of rapidly spinning black holes.

We consider a coherent fast magnetosonic wave propagating in the magnetosphere of a neutron star. In such an environment, the relative amplitude of the wave increases as it propagates away from the star, and will become nonlinear as the wave amplitude approaches the background magnetic field strength. We studied this transition using direct PIC simulations, and found that when the background magnetic field varies sufficiently slowly, the wave will launch a shock at every wavelength and dissipate a significant amount of energy into heating the plasma. I will discuss the implication of this study in the context of Fast Radio Bursts (FRBs), both to address whether an FRB produced in the inner magnetosphere can escape, and to propose a new mechanism for producing FRBs from low frequency fast waves launched by the neutron star.

While magnetic fields are important for angular momentum transport, gravity wave propagation, and astroseismology measurements in stellar radiative zones, the dynamo mechanism behind their generation remains an open problem. The extreme stable stratification characteristic of radiative zones imposes a particular form of anisotropy on the velocity field that generally suppresses dynamo action and is poorly understood. Returning to the fundamentals, I present studies of the effect of stable stratification on the small-scale dynamo and, in the additional presence of shear, the large-scale dynamo.  A novel instability criterion is determined, and their saturation is explored. Taking the solar radiative zone as a representative example, we find that the stratification is strong enough to make both the small-scale and large-scale dynamo marginally active in the stably stratified turbulence of the solar tachocline.

Magnetic reconnection can power bright and rapid flares originating from the inner magnetosphere of accreting black holes. We conduct extremely high resolution general-relativistic magnetohydrodynamics simulations, capturing plasmoid-mediated reconnection in a 3D magnetically arrested disk for the first time. We will show that an equatorial, plasmoid-unstable current sheet forms in a transient, non-axisymmetric, low-density magnetosphere within the inner ten Schwarzschild radii. Magnetic flux is expelled from the event horizon through reconnection at the converged universal plasmoid-mediated rate in this current sheet. The reconnection is fed by the highly-magnetized plasma in the jet, heating the plasma trapped in flux tubes to temperatures proportional to the jet's magnetization. Expelled flux tubes can orbit for an orbital period as low-density hot spots, in accordance with Sgr A* observations by the GRAVITY interferometer. Reconnection near the horizon produces sufficiently energetic plasma to explain flares from accreting black holes, such as the TeV emission observed from M87. The drop in mass accretion rate during the flare, and the resulting low-density magnetosphere make it easier for very high energy photons produced by reconnection-accelerated particles to escape. The extreme resolution results in a converged plasmoid-mediated reconnection rate that directly determines the timescales and properties of the flare.General relativistic magnetohydrodynamics (GRMHD) modeling is a powerful tool for describing the extreme plasma dynamics around compact objects including black holes. In such systems, the infalling plasma forms an accretion disk, which releases energy in the form of radiation, winds and Poynting-flux dominated jets. While GRMHD simulations have been successful in describing the large-scale plasma dynamics around slowly accreting black holes, the spatial scales on which dissipative processes are expected to converge were not resolved, which led to significant uncertainties in our understanding of non-thermal emission processes. On the other hand, the plasma around rapidly accreting black holes rapidly cools and collapses into a razor-thin disk, which is hard to resolve numerically and has presented an unsolved challenge for 3D GRMHD modeling. To tackle these and other challenging problems, I have developed the first graphics processing unit (GPU) accelerated radiative GRMHD code H-AMR and deployed it on the nation's largest supercomputer OLCF Summit. In the first part of my talk, I will discuss a wide range of algorithmic optimizations I have implemented in H-AMR to achieve excellent performance on a single GPU. I will then describe the load balancing routines and techniques I have developed to attain scalability (up to 6000 GPUs) on world's largest GPU clusters. In the second part of my talk I will highlight several groundbreaking discoveries enabled by global 3D GRMHD simulations with H-AMR: (i) self-consistent formation of multi-phase corona-like plasma in the presence of large scale magnetic flux, (ii) 3D plasmoid-mediated reconnection, and (iii) shredding of accretion disks by the frame dragging of rapidly spinning black holes.

The amplification of seed magnetic fields by the turbulent dynamo is believed to be essential in forming large-scale cosmic magnetic fields with dynamical strengths. The Weibel instability is a crucial mechanism that can produce seed fields from unmagnetized plasmas, but only at the plasma kinetic scale. It remains unclear whether such microscopic seed fields, under the joint action of their own nonlinear evolution and the background turbulence, can contribute to the formation of macroscopic magnetic fields. In the first part of this talk, I will demonstrate how an initially unmagnetized plasma may magnetize itself through the Weibel instability arising under the action of large-scale motions as simple as a shear-flow. The generation and nonlinear evolution of the Weibel seed fields are studied within a fully kinetic framework. For the second part, I will focus on our study of a system composed of an ensemble of magnetic flux tubes, the dynamics of which can represent the long-term evolution of filamentary Weibel seed fields. The formation of large-scale magnetic fields from initial small-scale fields and the associated inverse energy transfer have been identified as a result of the coalescence of magnetic structures through magnetic reconnection. An analytical model for the time evolution of quantities such as the magnetic energy and the energy-containing scale is constructed within the magnetohydrodynamic description, and is confirmed by our direct numerical simulations. In the end, we apply our study to estimate the length scale and strength of magnetic fields generated through this pathway to seed plasma dynamos.

Vlasiator (https://www2.helsinki.fi/en/researchgroups/vlasiator) is a high-performance kinetic code that is now performing the first ever 3D hybrid-Vlasov simulations of the global magnetospheric system. In the coming months, the driving conditions of these simulations will be scaled up to emulate the most extreme space weather events. These events are highly relevant in today's modern world, where electrical grids and satellites can be compromised by induced electric fields and particle fluxes. Called the "Carrington Project" after the famous storm of 1859 that lit up skies worldwide, our current work aims to answer the question: what if a Carrington-scale event were to happen today? Initial results of the 3D test runs will be shown to demonstrate that the code faithfully reproduces the features of near-Earth space under more modest driving conditions. This provides confidence that the upcoming simulations will accurately forecast the impacts of extreme storms on Earth's critical infrastructure.

Low temperature plasmas represent a unique non-equilibrium environment composed of neutral atoms and molecules, radicals, excited states, ions and electrons. These plasmas have characteristic electron energies of a few eV and can produce highly reactive chemistry at close to ambient temperatures. The resulting unique non-equilibrium conditions enable the delivery of highly reactive plasma species to heat sensitive surfaces and have enabled major advances in the microelectronics industry. More recently, developments at atmospheric pressure led to several emerging applications including wound healing, decontamination, water purification and chemical and material synthesis.

This seminar will provide an overview of the-state-of-the-art in the field of low temperature plasmas with a focus on atmospheric pressure plasmas interfacing with liquids. I will introduce the challenge of controlling plasma-liquid interactions. This includes key findings on plasma instabilities, self-organization at liquid interfaces and near interfacial (multiphase) species transport.

Acknowledgement: This work was partially supported by the US Department of Energy, Office of Science, Office of Fusion Energy Sciences, General Plasma Science program, under Award Number DE-SC-0016053 and DE-SC-0020232, the National Science Foundation under Award Number PHY 1903151, PHY 2020695 and CBET 1703439, and the Army Research Office under Grant Number W911NF-20-1-0105.

Grid instability growth rates of electrostatic particle-in-cell simulation algorithms, Luke Adams (CU)

An exhaustive study of grid-instability behavior in uniform drifting Maxwellian plasmas is presented for several explicit electrostatic particle-in-cell algorithms. Studied are the standard momentum conserving algorithm (MPIC), an energy conserving algorithm (EPIC), the Precise-Particle-in-Fourier method (PPIF), and a new cubic-spline based method (Particle-in-Cubic-Spline, PICS). The new PICS method has computational effort with ``PIC scaling'', while PPIF does not. MPIC and EPIC are studied for the three lowest-order shape functions. These methods are compared on the basis of accuracy, region of instability in the drift-velocity/temperature plane, instability growth rate, and particle noise.

Intermediate-Scale Zonal Flow Generation in Gyrokinetic-Ion Electron-Temperature-Gradient Simulations, Stefan Tirkas (CU)

The mechanism of anomalous electron heat transport in tokamaks is currently not well-understood. In fluid models, the zonal flow (ZF) generation by electron-temperature-gradient (ETG) turbulence is shown to be much weaker than that of similar ion ITG turbulence, leading to the expectation of a saturated state characterized by radially-elongated streamers at electron-gyroradius scales. However, gyrokinetic electron simulations have shown that ZF modes can contribute to long-time-scale behavior by breaking up these streamers into isotropic eddies. Recently, a toroidal, gyrokinetic-electron theory [1] has shown that, as the ETG spectrum cascades downward, a stronger Navier-Stokes type nonlinearity couples the intermediate-scale ETG-ZF modes, thus allowing for relevant ZF generation. We provide electron-scale, gyrokinetic, two-species simulation results from GENE, a 5-d gyrokinetic continuum code, with both single-mode ETG and full ETG spectra results comparing to the aforementioned theory. We will specifically look at the strength of ZF generation via ETG modes at intermediate and short-wavelength scales, as well as the role of collisionality in affecting the strength of the ZF generation.

[1] Haotian Chen et al 2021 Nucl. Fusion 61 066017.

Kinetic simulations of imbalanced turbulence in a relativistically-hot plasma, Lia Hankla (CU Affiliation)

Turbulent high-energy astrophysical systems often feature asymmetric energy injection: for instance, Alfven waves propagating from an accretion disk into its corona. Such systems are "imbalanced": the energy fluxes parallel and anti-parallel to the large-scale magnetic field are unequal. In the past, numerical studies of imbalanced turbulence have focused on the magnetohydrodynamic regime. In the present study, we investigate externally-driven imbalanced turbulence in a collisionless, ultrarelativistically hot, magnetized pair plasma using three-dimensional particle-in-cell (PIC) simulations. We find that the injected electromagnetic momentum efficiently converts into plasma momentum, resulting in net motion along the background magnetic field with speeds up to a significant fraction of lightspeed. This discovery has important implications for the launching of accretion disk winds. We also find that although particle acceleration in imbalanced turbulence operates on a slower timescale than in balanced turbulence, it ultimately produces a power-law energy distribution similar to balanced turbulence. Our results have ramifications for black hole accretion disk coronae, winds, and jets.

Ultracold neutral plasmas (UNPs) are an excellent experimental platform for measuring basic plasma properties.Their experimental parameters can be well-characterized, there are good available diagnostics, and their dynamics occur on experimentally-accessible timescales. We have conducted measurements of electron-ion collision rates in UNPs under conditions where electron strong coupling is relevant and separately as a function of electron magnetization from weak to extreme conditions. The measurement capabilities and our experimental results will present in this seminar, along with comparisons to theoretical predictions and how our results highlight important aspects of plasma theories.

Astrophysical plasma processes that occur in our Universe typically span orders of magnitudes in terms of time, length, and energy scales. As observers at Earth, we measure radiation produced during these processes in a variety of astrophysical environments. To correctly interpret these observations, we rely upon theoretical models that best describe the underlying plasma dynamics. And yet, no single model we possess can satisfactorily describe the wide spectrum of physical regimes to which plasmas are subjected. Over the past three decades, a plethora of theoretical models and numerical codes have been developed that describe specific ranges of spatial and temporal scales; in this talk I will review the efforts made to combine these single models into "hybrid", cross-scale and cross-physics tools capable of capturing plasma processes on many different levels and in vastly different regimes.

One of the key issues of present tokamak experiments and future fusion devices operating with high-Z materials as plasma-facing components, such as ITER, is to prevent and control high-Z impurities accumulation. Accumulation of heavy impurities such as tungsten (Z=74) in the inner core can have very deleterious effects on fusion performance due to large radiative power losses associated with line radiation. Thus, A reliable prediction of the temperature and density profile in the central region(rho < 0.3) is crucial for the control of W accumulation. Turbulent transport in the central region remains, however, largely unexplored.

In this work, turbulent transport analysis of the inner core of high-beta JET hybrid H- mode discharge #75225 is investigated through linear and nonlinear gyrokinetic simulations using the gyrokinetic code GKW in the local limit. The linear stability analysis indicates that Kinetic Ballooning Modes (KBM) dominate in the central region. A dedicated analysis performed at ρ = 0.15 reveals that the main parameters responsible for the destabilisation of KBMs in these hybrid H-modes are the high beta and low magnetic shear values. The KBMs are driven by the main ion pressure gradient. The study is then extended to the nonlinear regime. It is found that the turbulence induced by these KBMs drives a significant ion and electron heat flux.

I will discuss a crucial role that magnetic reconnection may play in magnetic plasma turbulence. It is known that given a large enough magnetic Reynolds number, turbulent flows generate anisotropic small-scale structures -- current sheets. I will argue that such current sheets can become unstable to tearing mode, which, in turn, modifies turbulence at the corresponding scales. As a result of this process, a new regime of tearing-mediated turbulence can be established.

3pm Gamow Tower F931 & Zoom
Young and active neutron stars may experience star quakes that can launch kHz Alfven waves into the magnetosphere. An Alfven wave packet propagating along the closed field lines undergoes several interesting nonlinear processes: (1) the Alfven wave can convert to fast magnetosonic waves that leave the magnetosphere; (2) the Alfven wave packet gets sheared due to the different lengths of neighboring field lines, leading to enhanced current that triggers kinetic instabilities; (3) Alfven waves propagating to the outer magnetosphere may break and form "plasmoids" (closed field loops) that accelerate away from the star. Most interestingly, the third process may be a viable mechanism to produce the simultaneous X-ray bursts and fast radio bursts from the galactic magnetar SGR 1935+2154. In this talk, I'll present our systematic study of these processes and discuss their observational consequences.

Turbulent high-energy astrophysical systems often feature asymmetric energy injection or driving, for instance nonlinear interactions between Alfvén waves propagating from an accretion disk into its corona. Such systems--relativistic analogs of the solar wind--are “imbalanced”: the energy fluxes parallel and anti-parallel to the large-scale magnetic field are unequal and the plasma possesses net cross-helicity. In the past, numerical studies of imbalanced turbulence have focused on the magnetohydrodynamic regime. In the present study, we investigate externally-driven imbalanced turbulence in a collisionless, ultrarelativistically hot, magnetized pair plasma using three-dimensional particle-in-cell simulations. We find that a turbulent cascade forms for every value of imbalance and that injected Poynting flux efficiently converts into net momentum of the plasma, with implications for the launching of a disk wind. Surprisingly, particle acceleration remains efficient even for very imbalanced turbulence. These results better characterize properties of imbalanced turbulence in a collisionless plasma and have ramifications for black hole accretion disk coronae, winds, and jets.

The design of modern stellarators with acceptable confinement properties requires numerical optimization of the magnetic field in the non-convex, high-dimensional spaces describing their geometry.  Another major challenge facing the stellarator program is the sensitive dependence of confinement properties on coil shapes, necessitating construction under tight tolerances. These challenges are addressed with the application of adjoint methods and shape sensitivity analysis. Adjoint methods enable the efficient computation of the gradient of a function that depends on the solution to a system of equations, such as linear or nonlinear PDEs. We present the first applications of adjoint methods for stellarator shape optimization. Several examples of this approach will be discussed, including the optimization of neoclassical properties based on the solution of an adjoint drift kinetic equation [1] and the optimization of equilibria based on the solution of an adjoint MHD force balance equation [2,3,4].  These advances enable a reduction in cost by several orders of magnitude over traditional optimization methods and provide additional insight into the local sensitivity of confinement properties.

[1] E. J. Paul, I. G. Abel, M. Landreman, W. Dorland, J. Plasma Phys. 85, 795850501 (2019).

[2] T. Antonsen, E. J. Paul, M. Landreman, J. Plasma Phys. 85, 905850207 (2019).

[3] E. J. Paul, T. Antonsen, M. Landreman, W. A. Cooper, J. Plasma Phys. 86, 905860103 (2020).

[4] E. J. Paul, M. Landreman, T. Antonsen, J. Plasma Phys. 87, 905870214 (2021).

On track to start construction in the second half of 2021, SPARC will be a compact, high-field, D-T fusing tokamak with ICRF auxiliary heating. The primary goal of SPARC is the demonstration of Q>2, and both empirical scalings and integrated simulations have been used to ensure that SPARC will be capable of realizing its mission. High fusion power and net-energy plasmas will be achieved in a compact (R=1.85m) device thanks to the high strength of the toroidal magnetic field (B=12.2T on axis), facilitated by new high-temperature superconductor technology. This talk will present the SPARC tokamak and will walk through the transport modeling techniques used during the design and the scoping of its main plasma scenarios.

Experimental efforts to study fusion and astrophysical plasmas have produced significant scientific advances but remain challenged by diagnostic access and limitations. Hence, there is a need for high-fidelity computational models to support experiments. A hierarchy of models, ranging from magnetohydrodynamic (MHD) to fully kinetic, are developed and applied across a wide range of parameter regimes in the Plasma Dynamics Computational Laboratory at Virginia Tech. This seminar will focus on high-energy-density plasma studies of hydrodynamic and magnetohydrodynamic instabilities relevant to fusion and astrophysical plasmas. The Rayleigh-Taylor instability (RTI) has been known to play a critical role in producing hydrodynamic mix at material interfaces, being particularly detrimental during the deceleration-phase of an inertial confinement fusion implosion. Self generated and externally-applied magnetic fields significantly impact RTI growth even for high-beta plasmas where the plasma pressure is many orders of magnitude greater than the magnetic pressure. More specifically, magnetic fields have the utility of damping instability growth if appropriately oriented with the interface thus providing a mechanism for mitigating hydrodynamic mix. Multi-fluid plasma simulations of hydrodynamic mix will be presented along with mix mitigation techniques which include viscous, ablative, and magnetic stabilization of RTI. The impact of transport and magnetic fields on RTI-induced turbulence will also be presented.

Magneto-inertial fusion (MIF) approaches seek to combine elements of both magnetic and inertial confinement concepts to enable high-yield fusion in the laboratory. In MIF, a magnetic field is applied in the fusion fuel plasma "target" to limit heat and particle transport rates, and the target is then further heated and compressed by an imploding "liner" or heavy shell of material. These approaches have attracted increased interest in recent years, particularly catalyzed by the very promising results of the MagLIF experiment from Sandia National Laboratories [1].

Plasma-jet-driven MIF (PJMIF) is an approach that seeks to combine the attractive heating and compression physics of MIF with a reactor-friendly facility configuration, in which the magnetized fusion fuel plasma and dense imploding liner are assembled from merging supersonic plasma jets at a several-meter "standoff" distance from all experimental hardware, enabling non-destructive and repetitive operation [2]. We are exploring this novel configuration at the Plasma Liner Experiment (PLX) at Los Alamos National Laboratory, having experimentally studied the merging of multiple plasma jets in relevant regimes [3, 4]. PLX has recently completed an upgrade to house a spherical array of 36 plasma jets, allowing the first studies of the assembly and convergence of spherically imploding plasma liners. In this talk I will give a brief summary of PLX results and discuss recent preliminary results with fully spherical plasma liner implosions.

1. Gomez, Matthew R., et al. "Experimental demonstration of fusion-relevant conditions in magnetized liner inertial fusion." Physical review letters 113.15 (2014): 155003.

2. Thio, YC Francis, Hsu, Scott C., et al. "Plasma-jet-driven magneto-inertial fusion." Fusion Science and Technology 75.7 (2019): 581-598.

3. Merritt, Elizabeth C., et al. "Experimental characterization of the stagnation layer between two obliquely merging supersonic plasma jets." Physical review letters 111.8 (2013): 085003.

4. Langendorf, Samuel J., et al. "Experimental measurements of ion heating in collisional plasma shocks and interpenetrating supersonic plasma flows." Physical review letters 121.18 (2018): 185001.

This work is supported by the Advanced Research Projects Agency -- Energy (BETHE program), U.S. Dept. of Energy under contract no. DE-AC52-06NA25396.

Many space and astrophysical plasmas, such as the solar wind, radiatively inefficient accretion flows onto black holes, and the intracluster medium of galaxy clusters (ICM), are hot and dilute, which makes them weakly collisional or even collisionless. We know from direct in-situ measurements (for the solar wind), radio and X-ray observations (for the ICM), and theoretical models alongside sub-mm observations (for the accretion flows) that these plasmas host a broadband spectrum of turbulent fluctuations. Kinetic processes, occurring on scales much smaller than what could realistically be observed from Earth, can influence the emission from these systems in two main ways. First, the emission itself is radiated primarily by electrons, which are heated by the turbulent cascade. Second, deviations from thermodynamic equilibrium caused by the turbulent motions could make the plasma unstable to a number of kinetic microinstabilities. These instabilities introduce an effective collisionality into otherwise collisionless plasmas and thereby impact the dynamics of turbulent fluctuations. In this talk, I will highlight recent results of kinetic modeling of collisionless turbulence. For low and moderate values of plasma beta (the ratio of thermal and magnetic pressures), the dissipation of turbulent fluctuations occurs at sub-ion-Larmor scales primarily through a combination of stochastic and ion-cyclotron heating. Our simulations of this regime reproduce the observed preferential perpendicular ion heating and the development of non-thermal beams in the ion distribution function seen in the solar wind. With our high-beta simulations, we explore the interplay between kinetic micro-instabilities and the turbulent cascade. In particular, we obtain the effective collisionality and viscous scale in collisionless high-beta turbulence.

Particle simulations of plasmas in the magnetosphere of compact objects are typically impeded by the limitations of available numerical algorithms. In particular, the need to resolve the gyro-motion of strongly articles (i.e. with microscopic gyro-radius) imposes severe constraints on standard particle pushers. As a consequence, the range of physical parameters (system size and/or time periods) that can be probed in particle-based magnetospheric simulations remains very limited in most cases. Here we present a new particle pusher designed specifically to overcome the need to resolve the particle gyro-motion of particles gyrating on microscopic scales, that do not contribute substantially to the system's evolution. For such particles, the new algorithm retains high accuracy by switching to a guiding-center formulation of the equations of motion. At the same time, particles whose gyro-radius becomes macroscopic after experiencing strong energization (e.g. in reconnecting current sheet) are accurately captured by switching to a standard Boris pusher. The dynamic coupling of the two numerical schemes allows for highly accurate particle simulations even when the time step exceeds the typical particle gyro-period by many orders of magnitude.

An emerging health problem is water contamination of our freshwater supplies, from waste derived from pharmaceuticals, personal care products, and industry. Health impacts to the public and aquatic life range from endochrine disruption to cancer. Advanced water- purification treatment of both domestic drinking water and treated waste water is needed because conventional water treatment methods are inadequate for the increasing trace amounts of these contaminants and because the resiliency of domestic water supplies against issues such as drought and infrastructure failure need to be improved. "Advanced oxidation", which introduces reactive oxygen species (ROS), such as ozone, hydrogen peroxide and hydroxyls, for degrading contaminants into harmless byproducts by a process known as mineralization, is a conventional solution but requires non-water consumables, i.e., chemicals. In contrast, introducing "plasma" to interact with the problem water can drive advanced oxidation without the need for non-water consumables and can be tailored to address a wide range of contaminants. In this talk, we review the threats to freshwater supplies, the shortcomings of conventional methods, and the promising solution posed by the interaction of plasma with water. Anecdotal cases of the effectiveness of this fascinating and effective approach to water treatment will be presented.

The recent generation of laboratory high-energy-density physics facilities has opened a significant new way to experimentally study the fundamental physics behind astrophysical plasmas.  I will review our progress on several challenge problems, including observation of magnetic reconnection mediated by plasmoid instabilities, laboratory generation and observations of magnetized collisionless shocks, first-principles simulations of magnetic field generation by Biermann battery and Weibel instability.  These processes are all of interest because they mediate energy exchange in plasmas between plasma flows (kinetic energy), thermal energy, and magnetic fields, and are can accelerate energized particles in cosmic plasmas, and may be responsible for production of high-energy cosmic rays.   Experiments are conducted at NIF and OMEGA and modeled with first principles particle-in-cell simulations using the PSC code, supported by INCITE.

Quantum computers show promise to solve some computational problems exponentially faster than classical computers. This naturally includes the simulation of quantum many-body systems, yet quantum algorithms can also achieve speedups for problems unrelated to quantum physics. For example, we find that a set of variables describing linear Landau damping evolves unitarily, which allows us to develop and test a quantum algorithm that can simulate this evolution efficiently. This approach could be extended to include electromagnetics, but incorporating nonlinearity is more challenging. We introduce a formalism for mapping nonlinear dynamical systems to infinite-dimensional, linear dynamical systems. When the resulting system can be truncated, yielding a finite linear system, quantum algorithms can be applied to perform the associated evolution. We consider the application of this strategy to the Vlasov-Poisson system.

Turbulent transport in the inner core of the high-JET hybrid discharge.

75225 is investigated extensively through linear and non-linear gyrokinetic simulations using the gyro-kinetic code GKW in the local approximation limit. Compared to previous studies [Citrin et al 2015 Plasma Phys. Control. Fusion 57 014032], the analysis has been extended towards the magnetic axis, rho<0.3 (rho is toroidal flux coordinate), where the turbulence characteristics remain an open question.

Understanding turbulent transport in this region is crucial to predict core profile peaking that in turn will impact the fusion reactions and the tungsten neoclassical transport, in present devices as well as in ITER. At rho= 0.15, a linear stability analysis indicates that Kinetic Ballooning Modes (KBMs) dominate, with an extended mode structure in ballooning space due to the low magnetic shear. The sensitivity of KBM stability to main plasma parameters is investigated. In the non-linear regime, the turbulence induced by these KBM modes drives a significant ion and electron heat flux. Standard quasi-linear models are compared to the non-linear results. The standard reduced quasi-linear models work well for the ExB part of heat flux, but fail to capture magnetic flutter contribution to the electron heat flux induced by the nonlinear excitation of low k_theta*rho_i (poloidal wave vector) micro-tearing modes (MTM) that are linearly stable. An extension of the quasi-linear models is proposed allowing better capturing the magnetic flutter flux.

Popular textbooks on electromagnetics such as Griffith's only present a single quasi-static limit of Maxwell's equations ("the quasi-static limit") while Jackson's textbook presents the magneto-quasi-static limit, and also Darwin's approximation with no discussion of the relationship of the two. To clarify these limits, a perturbation expansion is applied to the vacuum Maxwell equations to show that there are three quasi-static limits: the electro-quasi-static limit (EQS), the magneto-quasi-static (MQS), and the electromagnetic-quasistatic limits. The EQS and MQS limits are known as "Galilean electromagnetics", and the EMQS limit is known as the Darwin approximation. The forms for each quasistatic limit is present in the {local,global}, {field,potential} forms. The applicability to media with bound electrons is briefly discussed to provide an intuitive understanding when these limits are valid.  For media with unbound electrons, plasmas, it is shown that the MQS limit is the quasi-neutral approximation, and the EQS limit is applicable to sheaths. It is argued that viewing the quasineutral approximation as another form of the MQS limit is superior to the standard presentation of the quasineutral approximation.

Particle-in-Cell (PIC) methods are powerful and well-established tools for plasma simulations. The most-used PIC formulation is based on the explicit formulation of governing equations (Vlasov + Maxwell equations). It has the property of conserving the total momentum of the system but not the total energy. On the contrary, a basic implicit discretization of the governing equations leads to a numerical scheme that conserves the total energy but not the total momentum. Implicit Energy-Conserving PIC methods have less demanding numerical constraints on the time step and grid spacing choice than explicit Momentum-Conserving PIC methods at the cost of higher computational complexity. Implicit Energy-Conserving PIC methods with large time steps rely on numerical collisionality to retain numerical stability, ultimately modeling the plasma as a fluid. For this reason, implicit Energy-Conserving PIC methods are said to bridge the kinetic and fluid approaches. In this talk, I will first introduce a basic formulation of an implicit Energy-Conserving PIC method. I will then describe a straightforward implementation based on Jacobian-Free Newton-Krylov non-linear solver and discuss the Energy-Conserving PIC properties that make them amenable for large-scale plasma simulations.

Magnetized Liner Inertial Fusion (MagLIF) is a fusion concept that involves imploding an initially solid cylindrical metal liner (Aluminum, Copper, or Beryllium) on to a pre-magnetized Deuterium-Tritium (D-T) fuel target.[1] The most detrimental instability toward achieving net gain is the magneto Rayleigh-Taylor instability (MRT) that occurs at the accelerating liner-vacuum interface during implosion.[2] Peterson et al. suggests that the electrothermal instability (ETI) seeds the MRT instability early on in the experiment.[3] This presentation describes ETI modeling using resistive-magnetohydrodynamics codes in MagLIF-relevant regimes, and presents a sensitivity analysis that impacts ETI growth. Furthermore, anomalous resistivity can significantly impact ETI and some preliminary studies of this will be discussed.

[1] S. A. Slutz, et al., Pulsed-power-driven cylindrical liner implosions of laser preheated fuel magnetized with an axial field), Physics of Plasmas 17 (2010). URL: http://scitation. aip.org/content/aip/journal/pop/17/5/10.1063/1.3333505. doi:http://dx.doi.org/10.1063/1.3333505.

[2] D. B. Sinars, et al., Measurements of magneto-rayleigh-taylor instability growth during the implosion of initially solid metal liners, Physics of Plasmas 18 (2011) 056301. URL: http://aip.scitation.org/doi/abs/10.1063/1.3560911. doi:10.1063/1.3560911. arXiv:http://aip.scitation.org/doi/pdf/10.1063/1.3560911.

[3] K. J. Peterson, D. B. Sinars, E. P. Yu, M. C. Herrmann, M. E. Cuneo, S. A. Slutz, I. C. Smith, B. W. Atherton, M. D. Knud- son, C. Nakhleh, Electrothermal instability growth in magnetically driven pulsed power liners, Physics of Plasmas 19 (2012) 092701.

The sparking of grapes in a household microwave oven has been a popular, if poorly explained online pop-sci phenomenon for decades. At first glance, simple explanations that treat wet grape skins as conductive antennas would seem to suffice. However, after years of playful investigation by a roster of undergraduate students, we now know that the explanation is far richer and expansive. Using thermal imaging, ultrahigh-speed videography, and computer simulations we have been able to establish a photonic explanation for the phenomenon that reveals the nature of cm-sized aqueous objects to act as dielectric microwave resonators. In this talk I will discuss how viewing grapes as spherical water in a vacuum both provides a satisfying resolution to the “fruit plasma” mystery and provides new opportunities for research in nano-photonics and soft-matter technologies.

Using direct Particle-in-Cell (PIC) simulations we study the propagation of Alfven waves into a low density plasma which cannot support the current required by the wave. We developed a simple analytic model to predict the behavior of the plasma, and use it to compute the dissipation rate and resulting particle Lorentz factors. I will describe the model in detail, compare it with numerical simulations, and comment on the implications on astrophysical scenarios such as magnetar flares and fast radio bursts.

Plasma occurs in a variety of aerospace systems including very high speed hypersonic vehicles and space electric propulsion systems. Development and application of high fidelity computational models are described for analyzing these low-temperature plasmas. For hypersonic vehicles, plasma is generated by chemical processes activated in the very high temperature air. The plasma may be used for flow control but can also lead to radio blackout. In space electric propulsion systems, plasma is generated and accelerated using a variety of mechanisms. Plasma models are used to understand basic operation and limitations of these devices. Opportunities for future plasma research in these areas are discussed.

Streaming plasma instabilities are ubiquitous in astrophysical plasma environments and are widely thought to underpin the physics of relativistic outflows in powerful astrophysical objects (e.g. gamma-ray bursts, active galactic nuclei, etc.). When an electron beam propagates through a plasma, return currents are established by the background plasma electrons. The resulting counterstreaming system of beam and plasma electrons is unstable to electromagnetic perturbations, which leads to the generation of strong electromagnetic fields. As a result, the relativistic particles in the beam experience large electromagnetic fields, and thus can emit bright bursts of gamma rays. Here we show that when high energy (10 GeV) and high peak current (> 100 kA) electron beams propagate in plasmas from gas to solid density, there is a growth and interplay between the current filamentation instability (CFI) and oblique mode, and that they strongly depend on the bunch length, the bunch density and the plasma collisionality. These processes are under study in the context of the E-305 experiment at the SLAC FACET-II facility, where such extreme beams will be available to explore this novel physics. We also report on the experimental probing of strong magnetic field fluctuations generated by the current filamentation instability in femtosecond laser-solid interaction [arXiv:1907.12052], where the instability arises from the counterstreaming of forward-directed, laser-accelerated fast electrons and the current-neutralizing, cold plasma electrons, and is probed at femtosecond time scales with electron beams from a laser wakefield accelerator.

An OMFIT [https://omfit.io] integrated modeling workflow capable of finding the steady-state solution with self-consistent core transport, pedestal structure, current profile, and plasma equilibrium has been developed and applied to DIII-D and ITER discharges. Key features of the workflow are: (1) Self-consistent modeling of impurity transport reduces the number of free parameters and assumptions that are used in the simulations; (2) Fast yet accurate simulations by leveraging neural network based models for the pedestal structure, and turbulent and neoclassical transport; (3) Full compatibility with the ITER Integrated Modeling and Analysis Suite (IMAS) achieved by transferring information among the different physics components with the newly developed OMAS library [https://gafusion.github.io/omas].

The large mass asymmetry between electrons and ions is a key element of the rich complexity for which plasma physics is well known. Correspondingly, the behavior of "pair plamsas", comprising negatively and positively charged particles of equal mass, is predicted to be markedly simpler in a number of ways. Not so simple, unfortunately, are the options for creating and studying such plasmas in the laboratory. This talk will describe the approach being pursued by the APEX (A Positron Electron eXperiment) collaboration, along with recent milestones and latest developments toward the goal of magnetically confined e+e- pair plasmas.

The extremely energetic class of astrophysical phenomena - including high-energy pulsar winds, gamma ray bursts, and jets from galactic nuclei - have plasma conditions where the energy density of the magnetic fields exceeds the rest mass energy density (sigma_cold = B^2/(mu_0 n_e m_e c^2), the cold magnetization parameter). Laboratory studies of magnetic dynamics provide an important platform for testing theories and characterizing different regimes. In this seminar, I will present experimental measurements, along with numerical modeling, of short-pulse, high-intensity laser-plasma interactions that produce extremely strong magnetic fields (>100T). Three-dimensional particle-in-cell simulations show the plasma density and magnetic field characteristics can satisfy "sigma_cold > 1". The generation and the dynamics of these magnetic fields under different target conditions was studied using proton radiography, and relativistic intensity laser-driven, magnetic reconnection experiments were performed. Evidence of magnetic reconnection was identified by the plasma?s X-ray emission patterns, changes to the electron spectrum, and by measuring the reconnection timescales. [A. E. Raymond, et al., PastePhysical Review E, 98, 043207 (2018)]

Within the Exascale Computing Program (ECP), the High-Fidelity Whole Device Modeling (WDM) project aims at delivering a first-principle-based computational tool that simulates the plasma neoclassical and turbulence dynamics from the core to edge of Tokamak. To permit such simulations, different gyrokinetic codes need to be coupled, which will take advantage of the complementary nature of different applications to build the most advanced and efficient whole volume kinetic transport kernel for WDM. Here we present that the two existing particle-in-cell (PIC) gyrokinetic codes GEM and XGC have been successfully coupled, where GEM is optimized for the core and XGC is optimized for the edge plasma. The current GEM-XGC coupling adopts a coupling scheme, which is initially developed using XGCcore-XGCedge coupled simulations [1]. In this scheme, the time-stepping of the global core and edge distribution functions is achieved by pushing the composite distribution function independently in each code, but using the common global potential field solution for the whole domain. Due to the different grids, an interpolation scheme is used for transferring data back and forth between GEM?s structured grid and XGC?s unstructured grid. Meanwhile, the whole coupling framework is based on the high-performance ADIOS library with its state-of-the-art dataspaces in file/memory coupling capability.

As linear electron beam accelerators continue to push towards larger energy densities, it will become necessary to focus these electron beams to even smaller spot sizes. For example, the matching condition for plasma wakefield accelerators (PWFA) operating at densities greater than 10^16 cm^-3 demands electron beam sizes which are very challenging to meet with conventional quadrupole magnets. These requirements can be met by using thin, passive plasma lenses to focus relativistic electron beams by taking advantage of the strong electromagnetic forces in the plasma. To achieve the precise plasma density profiles necessary for thin plasma lenses, a compressed femtosecond laser pulse of moderate energy is used to laser-ionize a region of uniform gas or the outflow of a gas jet. Here I will discuss applications of these thin, passive plasma lenses, second-order effects and aberrations they can produce, and future experimental plans for these lenses in the linear accelerator at SLAC's FACET-II facility.

We consider an initially laminar state and we ask the questions: what is the effect that the reconnection process has on the generation of turbulence and on the energy exchanges? And what is the relationship of turbulence and energy exchanges? In Nature, reconnection and turbulence are often interlinked and turbulence can itself cause the conditions for the onset of reconnection. But we consider here opposite problem: what is the feedback that reconnection has back on turbulence? Does it itself generate a turbulent cascade that can feed energy back towards larger scales? And what is rate effect on particle-field energy exchange. The progress we report comes from state of the art 3D simulations done with massively parallel particle In cell simulations where both electrons and ions are tracked as particles and where the resolution is sufficient to resolve electron and ion scales. Part of the work reported was recently published [1] [1] Lapenta, G., Pucci, F., Goldman, M. V., & Newman, D. L. (2020). Local regimes of turbulence in 3D magnetic reconnection. The Astrophysical Journal, 888(2), 104.

Warm Dense Matter is challenging to model in part due to the many simultaneous physical effects involved. In particular, Coulomb coupling and electron degeneracy have proven difficult to concurrently incorporate into models of dense plasmas. In this talk I present transport calculations based on the quantum Boltzmann equation of Uehling and Uhlenbeck, in which the electrons are subject to diffraction and Fermi degeneracy. The strategy involves modifying the equation to additionally incorporate correlations due to Coulomb coupling by specifying that the binary interaction be mediated through the statistical potential of mean force instead of the Coulomb potential. While a classical analog of this model applicable to ion transport was derived rigorously [Baalrud and Daligault, Phys. Plasmas 26, 8 (2019)], the quantum generalization of this derivation for electron transport presents further difficulties. Instead of a derivation, I take the presence of the potential of mean force as a postulate. This potential derives from the equilibrium structure of the plasma and in this case is furnished by an existing model that couples the correlation functions of the plasma with an average-atom model for the quantum state of the ions. I evaluate the equation to predict electron-ion momentum relaxation rates in dense hydrogen and aluminum plasmas, and compare the electrical conductivities derived from these rates to simulations and experimental measurements. This serves to illuminate the relative impact of diffraction, degeneracy, Coulomb correlation, electron-electron collisions, and large-angle scattering on collisional transport.

Rapid gamma-ray flares pose an astrophysical puzzle, requiring mechanisms both to accelerate energetic particles and to produce fast observed variability. These dual requirements may be satisfied by collisionless relativistic magnetic reconnection. On the one hand, relativistic reconnection can energize gamma-ray emitting electrons. On the other, as previous kinetic simulations have shown, the reconnection acceleration mechanism preferentially focuses high-energy particles -- and their emitted photons -- into beams, which may create rapid blips in flux as they cross a telescope's line of sight. Using a series of 2D pair-plasma particle-in-cell simulations, we explicitly demonstrate the critical role played by radiative cooling in mediating the observable signatures of this `kinetic beaming' effect. Only in our efficiently cooled simulations do we measure kinetic beaming beyond one light crossing time of the reconnection layer. We find a correlation between the cooling strength and the photon energy range across which persistent kinetic beaming occurs: stronger cooling coincides with a wider range of beamed photon energies. We also apply our results to rapid gamma-ray flares in flat-spectrum radio quasars, suggesting that a paradigm of radiatively efficient kinetic beaming constrains relevant emission models. In particular, beaming-produced variability may be more easily realized in two-zone (e.g. spine-sheath) setups, with Compton seed photons originating in the jet itself, rather than in one-zone external Compton scenarios.

Magnetic reconnection is a physical process whereby a sudden change in the topology of magnetic field lines allows magnetic energy to be converted into particle heating and acceleration, often resulting in explosive events observed in astrophysical as well as in laboratory plasmas. Essential to explain for solar flares, coronal mass ejections and the energization in the Earth’s and planetary magneto- spheres, it also plays a fundamental role in explosive energy release in pulsar nebulae, gamma-ray bursts and it has been observed in sawtooth crashes in tokamaks, finally becoming the focus of several laboratory experiments. I will summarize what we know about the physics of the onset of magnetic reconnection and how we observe it in laboratory as well as in space and astrophysical plasmas. I will explain why a full understanding of the onset problem is important to study the dynamics of reconnection itself and particle heating and acceleration, placing it in the context of the plasma evolution and topology in the solar corona and the magnetosphere. I summarize what we know up to now on the onset of reconnection in partial ionized plasmas in fluid and kinetic regimes.

Finally I will talk about the FLARE experiment and how it can address the onset of reconnection in laboratory plasma, helping to understand fluid vs kinetic modeling of reconnection onset.

To probe physical conditions in the atmosphere of the Sun we have to rely on remote sensing. Therefore, we have to understand and be able to model a variety of physical processes that contribute to the formation of the solar spectra. To perform reliable diagnostics we need realistic models, as well as inverse methods that allow us to infer model parameters from the observed polarized spectra. The new generation solar telescopes such as DKIST will make this problem especially challenging since the amount of data to be interpreted will increase by an order of magnitude (or more). In this talk we will discuss spectral line formation in the solar atmosphere and the physical mechanisms responsible for polarization in spectral lines. We will then turn to the inference methods that allow us to fit atmosphere models to the observed polarized spectra and to estimate temperatures, velocities and magnetic fields in the atmosphere of the Sun. We will put this all in the context of the DKIST solar telescope that just delivered the first-light images, and discuss the challenges it will bring to scientists working on theory and spectral diagnostics.

This talk discusses a new parametric instability mechanism caused by particles that are ?weakly trapped? in the potential wells of a nonlinear wave[1].The mechanism applies to low-collisionality ?Vlasov? plasmas supporting waves with near-acoustic dispersion relations such as ion sound waves, magnetized Langmuir waves, electron acoustic waves, or Alfven waves. The theory is compared to particle in cell [PIC] simulations of Trivelpiece-Gould [TG] waves, as well as to experiments[2] on pure ion plasmas that observe parametric instability in TG standing waves. For TG waves, the standard parametric instability mechanism[3] induced by wave-wave coupling is suppressed. The new mechanism predicts instability only if weakly trapped particles are present, at rates found to be in agreement with the simulations, and consistent with the experiments. In the parametric instability studied here, a nonlinear ?pump? wave is unstable to the growth of daughter waves with twice the wavelength and nearly the same phase velocity as the pump. This induces adjacent potential peaks in the wave to slowly approach one-another, receding from other pairs of peaks. Particles that are weakly trapped between approaching peaks, with kinetic energies just below the potential maxima, are heated by compression and escape the well, and then become retrapped on the other side of the approaching peaks, where they amplify the compression by pushing the peaks together. Distributions with weakly trapped particle populations (appearing as phase space ?holes? or ?rings? in the trapped particle distribution) often occur in nonlinear plasma waves and BGK states, and such distributions can be unstable to this new trapped particle mechanism. [1] D. Dubin, Phys. Rev. Lett. 121, 015001 (2018); D.. Dubin, Phys. Plasmas 26, 102113 (2019). [2] F. Anderegg, M. Affolter, A. Ashourvan, D. Dubin, F. Valentini and C. F. Driscoll, Phys. Rev. Lett. 121, 235004 (2018); M. Affolter, F. Anderegg, D. H. E. Dubin, F. Valentini, and C. F. Driscoll ,, Phys. Plasmas , accepted (2019). [3] See, e.g., R. Sagdeev and A. Galeev, ?Nonlinear Plasma Theory?, (Benjamin, N.Y., 1979).

Magnetic reconnection events are typically two-timescale processes: an initial, slow stage of energy accumulation, followed by a rapid stage of energy release. The transition between these two stages ? the so-called reconnection onset ? is a poorly understood process; it is, however, critical, in that it determines the energy available for release in the reconnection event. In this talk, I will present a conjecture for how the onset occurs, based on current sheet instabilities which develop as the current sheet forms. I will illustrate how to compute the onset moment, and the reconnection parameters at that moment, in the MHD framework. The collisionless case is more subtle and requires further considerations; certain key aspects of this will also be discussed.

Nonthermal relativistic plasmas are ubiquitous in astrophysical systems like pulsar wind nebulae and active galactic nuclei, as inferred from their emission spectra. The underlying nonthermal particle acceleration processes have traditionally been modeled with a Fokker-Planck diffusion-advection equation in momentum space. In this talk we discuss tests of such particle acceleration models in particle-in-cell (PIC) simulations of driven magnetised turbulence in relativistic pair plasma. Our work takes advantage of the microphysical information available in PIC simulations including the self consistent particle trajectories and energy histories. Hence we are able to test whether particle energies indeed diffuse over time, and subsequently measure the diffusion and advection coefficients as a function of particle energy. We then discuss extensions to this type of diagnostic, as well as ongoing efforts to apply this and other measurements to better understand the mechanisms of nonthermal particle acceleration.

One of the hallmarks of the electron diffusion regions (EDRs) at the core of magnetic reconnection in Earth’s magnetosphere – a primary focus of NASA’s four-spacecraft Magnetospheric MultiScale (MMS) mission – is the presence of agyrotropic electron distributions characterized as “crescents.”  A useful testbed for studying plasma dynamics in the presence of measured distributions is to initialize simulations with self-consistent kinetic equilibria based on the satellite observations. However, because agyrotropy is incompatible with spatial uniformity in a steady state, such equilibria are necessarily inhomogeneous.  Methods for modeling the observed electron distributions and designing self-consistent kinetic equilibria will be presented.  Aspects of the dynamical evolution of “crescent-equilibria” will also be illustrated using PIC simulations initialized with model agyrotropic distributions.

The majority of Solar System planets possess global-scale, self-generated magnetic fields. These fields are generated by the dynamo process, whereby the kinetic energy of an electrically-conducting fluid is converted to electromagnetic energy. Such fluids are driven primarily by buoyancy and evolve under the constraints imposed by rotation, through the action of the Coriolis force, and magnetic fields. In this talk the theory of buoyancy-driven flows in the presence of magnetism and rotation, as applicable to the dynamics of planetary interiors, will be discussed, coupled with results from ongoing modeling efforts.

Characterizing magnetic reconnection regions using Gaussian mixture models on particle velocity distributions from simulations: We present a method based on unsupervised machine learning to identify regions of interest using electron velocity distributions as a signature pattern. An automatic density estimation technique is applied to particle distributions provided by PIC simulations to study magnetic reconnection h. This method identifies automatically the presence of complex distributions due to beams or other non-Maxwellian features and can be used as a detection algorithm able to identify reconnection regions. The method is also compared to more physical plasma properties: Swisdak's agyrotropy parameter. The approach is demonstrated for specific double Harris sheet simulations but it can in principle be applied to any other type of data in the future, in particular 3D simulations.

Dwarf novae are accreting compact binaries that exhibit eruptions lasting approximately a week with a recurrence time scale of a month. Eruptions are thought to be due to a thermal-viscous instability in the accretion disk surrounding the white dwarf. This model has long been known to put constraints on the mechanisms transporting angular momentum in the disk. Traditionally, transport is presumed to be turbulent where turbulence is due to the magneto-rotational instability (MRI). However, I show here, using local simulations of accretion disks with radiative transfer that there exists a discrepancy between observations and light curves obtained supposing MRI turbulence only. In quiescence, where the disk is poorly ionized, it is very unlikely that MRI can even survive. However, a number of MHD simulations show that transport of angular momentum could also be driven by MHD outflows. Wind-driven transport is, by nature, very different from turbulent transport; it induces a surface-torque on the disk and does not deposit thermal energy locally but extracts energy from the disk instead. We included MHD wind-driven angular momentum transport in a disk instability model, a model which is usually used to reproduce light curves of dwarf novae. With this new model, we were able to retrieve light curves looking like observations, using a fixed magnetic field configuration in the disk. It is the first time that eruptions of dwarf novae are modeled with success using prescriptions for angular momentum transport derived from first principles instead of ad hoc parameters.

Magnetic reconnection is a fundamental plasma process that rapidly converts magnetic energy to particle kinetic energy. It has been studied mostly in nonrelativistic electron-ion plasmas relevant to the solar corona, Earth's magnetosphere, and lab plasmas. However, reconnection in collisionless relativistic electron-ion and electron-positron (pair) plasmas may be important in astrophysical systems such as pulsar wind nebulae and black-hole jets, and is, moreover, more amenable to first-principles particle-in-cell (PIC) simulation. A striking consequence of relativistic reconnection is efficient nonthermal particle acceleration (NTPA). The power-law energy distributions of electrons (and positrons) accelerated by reconnection should emit distinctive, observable synchrotron and/or inverse Compton radiation signatures. Even in environments where accelerated particles promptly radiate away most energy gains, self-consistent radiative-PIC simulations show that reconnection still functions efficiently. While reconnection-driven NTPA has been studied in 2D simulations over a broad range of plasma conditions, a critical question is whether reconnection behaves similarly in 3D. Large 3D PIC simulations show that, in the magnetically-dominated ultrarelativistic pair regime, reconnection and NTPA are similar in 2D and 3D. However, when the magnetic energy is comparable to the plasma energy, reconnection slows and is disrupted by 3D effects like the relativistic drift-kink instability; nonetheless, NTPA remains robust even as reconnection dynamics alter significantly.

In this talk, I will be preoccupied with two main themes: Are there universal collisionless equilibria, or classes thereof, and how do we determine them? What is the structure of phase-space turbulence? Making progress on the first question turns out to depend on having an answer to the second. On the second question, there is some recent, interesting news: I will show how one might go about deriving a universal phase-space spectrum of collisionless plasma turbulence and how the outcome leads one to conclude that Landau damping (phase mixing) is suppressed in nonlinear plasma systems [1-4]. I will then outline a programme for deriving "collisionless collision integrals" and speculate about what the result will look like: turbulent plasmas may turn out to be effectively quite collisional. [1] T. Adkins and A. A. Schekochihin, J. Plasma Phys. 84, 905840107 (2018) [2] A. A. Schekochihin et al., J. Plasma Phys. 82, 905820212 (2016) [3] J. T. Parker et al., Phys. Plasmas 23, 070703 (2016) [4] R. Meyrand et al., PNAS 116, 1185 (2019) 

A wide range of space and astrophysical systems, such as the solar corona, heliosheath and Weibel-produced magnetic field in supernova shocks, of which the dynamics are governed by turbulence and reconnection, can be conceptualized as an ensemble of interacting flux ropes. We investigate magnetic field dynamics in a system of parallel flux ropes as well as more generic magnetically-dominated turbulent systems, focusing on the inverse magnetic energy transfer. An analytical model is introduced and shown to capture the evolution of the main quantities of interest, as borne out by our 2D and 3D reduced magnetohydrodynamics (RMHD) and 2D particle-in-cell simulations. Magnetic reconnection is identified as the key mechanism enabling the inverse transfer and setting its properties: magnetic energy decays as t^-1, where t is time normalized to the reconnection timescale; and the field correlation length grows as t^1/2. Critical balance is shown (by magnetic structure functions) to govern the aspect ratio of the flux ropes in 3D RMHD simulations. This quantitative description of inverse energy transfer could improve our understanding of longstanding problems such as coronal heating, galactic magnetogenesis, and high-energy emission in gamma-ray bursts.

Electron velocity distribution functions in the solar wind according to standard models consist of 4 components, of which 3 are symmetric - the core, the halo, and the superhalo, and one is magnetic field-aligned, beam-like population, referred to as the strahl. We analysed in-situ measurements provided by the two Helios spacecrafts to study the behaviour of the last, the strahl electron population, in the inner Solar system between 0.3 and 1 au. The strahl is characterised with a pitch-angle width (PAW) depending on electron energy and evolving with radial distance. We find different behaviour of the strahl electrons for solar wind separated into types by the core electron beta parallel value. For the low-beta solar wind the strahl component is more pronounced, and the variation of PAW is electron energy dependent. In the high-beta solar wind the strahl appears broader in consistence with the high-beta plasma being more unstable with respect to kinetic instabilities. As a continuation of this project we tried to quantify the effect of Coulomb collisions on the electron velocity distribution function using a fully kinetic model of radially expanding solar wind taking into account binary collisions between particles.

Solar and stellar flares are the most intense emitters of X-rays and extreme ultraviolet radiation in planetary systems. On the Sun, strong flares are usually found in newly emerging sunspot regions. The emergence of these magnetic sunspot groups leads to the accumulation of magnetic energy in the corona. When the magnetic field undergoes abrupt relaxation, the energy released powers coronal mass ejections as well as heating plasma to temperatures beyond tens of millions of kelvins. While recent work has shed light on how magnetic energy and twist accumulate in the corona and on how three-dimensional magnetic reconnection allows for rapid energy release, a self-consistent model capturing how such magnetic changes translate into observable diagnostics has remained elusive. Here, we present a comprehensive radiative magnetohydrodynamics simulation of a solar flare capturing the process from emergence to eruption. The simulation has sufficient realism for the synthesis of remote sensing measurements to compare with observations at visible, ultraviolet and X-ray wavelengths. This unifying model allows us to explain a number of well-known features of solar flares, including the time profile of the X-ray flux during flares, origin and temporal evolution of chromospheric evaporation and condensation, and sweeping of flare ribbons in the lower atmosphere. Furthermore, the model reproduces the apparent non-thermal shape of coronal X-ray spectra, which is the result of the superposition of multi-component super-hot plasmas up to and beyond 100 million K. Cf. M. C. M. Cheung, M. Rempel, & HGCR Science team, Nature Astronomy, 3(2), 160 (2019)

The advent of high-cadence, large-scale photospheric vector magnetic field and Doppler velocity measurements from the Solar Dynamics Observatory and progress in the computational techniques have facilitated development of the time-dependent data-driven models of the coronal magnetic fields. In this talk I will first review current state and challenges of these models. I will then describe recent progress of the Coronal Global Evolutionary Model (CGEM), a collaborative effort between UC Berkeley, Lockheed Martin and Stanford University that computes electric fields in the photosphere to drive a 3D non-potential model of the solar corona magnetic fields. Finally I will tell how observations from DKIST, the largest solar telescope in the world, would help to move these data-driven models forward.

Existing theoretical and observational constraints on the abundance of magnetic monopoles are limited. In this talk, we will demonstrate that an ensemble of monopoles forms a plasma whose properties are well determined. The collective effects -- the benchmark of an electromagnetic plasma -- place new tight constraints on the cosmological abundance of monopoles. In particular, the existence of micro-Gauss magnetic fields in galaxy clusters and radio relics implies that the cosmological density parameter of monopoles is well below unity, which precludes them from being the dark matter. Furthermore, we will discuss that the monopole plasma may reveal itself on the sky as "zebra patterns" of an alternating magnetic field and may even be responsible for origin of the observed magnetic fields in galaxy clusters.

A double layer has been observed to form in the lab when a plasma flows along diverging magnetic field lines from a region of high field to a region of low field. This localized potential drop accelerates ions and retards electrons. A gyrofluid model and a gyrokinetic "exospheric" model have been developed and applied to this flow. These models include the electrostatic and mirror forces and for ions gravity is added. The potential drop across the layer cannot simultaneously satisfy the needs for quasineutrality downstream and current neutrality. However, a third particle population of cold returning "core" electrons can make the flow current-neutral so that all constraints are satisfied. This study grew from asking the following question: Does the fraction of solar wind electrons with sunward velocity vectors travel all the way back to the sun and subtract from the net loss of electrons? R. Boswell, E. Marsch, and C. Charles, /Astrophys. J./ 640, L199-L202 (2006) S. Robertson, /Physics of Plasmas/ 23, no. 4, 043513 (2016). S. Robertson, /IEEE Transactions on Plasma Science/ 45, no. 10, 2814-2819 (2017).

The standard particle-in-cell algorithm suffers from finite grid errors which break energy conservation, cause numerical dispersion, and create numerical instabilities. There exists a gridless alternative which bypasses the deposition step and calculates each Fourier mode of the charge density directly from the particle positions. We show that a gridless method can be computed efficiently through the use of an Unequally Spaced Fast Fourier Transform (USFFT) algorithm. After a spectral field solve, the forces on the particles are calculated via the inverse USFFT (a rapid solution of an approximate linear system). We provide one and two dimensional implementations of this algorithm with an asymptotic runtime of $O(N_p + N_m^D\log N_m^D)$ for each iteration, identical to the standard PIC algorithm (where $N_p$ is the number of particles and $N_m$ is the number of Fourier modes, and $D$ is the spatial dimnesionality of the problem). We demonstrate superior energy conservation and reduced noise, as well as convergence of the energy conservation at small time steps.

In this talk, I will describe the gyrokinetic (GK) electron and fully kinetic (FK) ion particle (GeFi) simulation model and the particle simulation results of waves and current sheet instabilities. In the GeFi model, the GK electron approximation removes the high frequency electron gyromotion and plasma oscillation, but the electron finite Lamor radii effects are retained. For lower-hybrid wave and kinetic Alfven wave, the GeFi results agree well with the fully kinetic explicit $\delta f$ code and the fully kinetic Darwin particle code. Our 3-D GeFi and FK simulation results demonstrate the existence of the lower-hybrid-drift, kink and sausage instability under finite guide magnetic fields with the realistic proton-to-electron mass ratio. The instability growth-rates are obtained as a function of k.

Highlights of recent laboratory studies of magnetic reconnection on MRX (Magnetic Reconnection Experiment) are summarized in comparison with space observations and numerical predictions. These include magnetic reconnection with asymmetry or guide field, various wave activity in and near the local X-line, energy conversion from magnetic field to plasma, and effects of partial ionization. The line-tied and arched flux rope stability is also studied in relation to Coronal Mass Ejections observed on the Sun. The next step device, FLARE, which achieved its first plasma in 2018, will be described for the planned laboratory experiments in the near future.

Magnetic energy transfer from small to large scales is considered an important process which may explain the existence of galactic magnetic fields with large sclare coherent structures and microgauss strengths. We investigate a mechanism for inverse energy transfer by studying the long time evolution of a system consisting of parallel current filaments (corresponding to magnetic islands). An analytical model is introduced to describe the inverse energy transfer with the heirarchical merger of magnetic islands through successive reconnection events. Reduced MHD simulations are conducted to confirm the analytical model and explore the self-similar properties of the system.

In recent years, open source packages such as Astropy and SunPy have been fundamentally changing the way scientific research is done intheri respective fields. PlasmaPy is a newly openly-developed community Python package that is working to fill this role for plasma physics. This project strives to provide the core functionality that is needed to foster the creation of a fully open source Python ecosystem for heliospheric, laboratory, and astrophysical plasmas that is compatible with Astropy and SunPy. Our first development release includes the calculation of plasma parameters and transport coefficients, methods for accessing atomic data, and the prototype of a class to describe arbitrary plasmas. Upcoming releases will include numerical simulation and observational/experimental analysis capabilities, as well as tools for plasma theory. In this talk, I will present modern best practices for scientific computing that we are adopting in PlasmaPy, describe PlasmaPy's current and planned capabilities, and duscuss how our community can work together to forge an open source software ecosystem.

Magnetic reconnection is a commonly known multi-scale plasma process that quickly converts magnetic energy into kinetic energy in bulk plasma flow, thermal and nonthermal particle distributions. An important problem that remains unsolved is the acceleration of nonthermal charged particles in the reconnection region. In particular, the large-scale theory and 3D extension of this problem are poorly known. To shed more light on this problem, we utilize a number of tools. Using LANL’s VPIC code, we study particle acceleration in magnetic reconnection via large-scale 3D kinetic simulations to examine several effects that may be important, including pre-existing fluctuations, kink and secondary tearing instabilities, and open boundary conditions. The results show that particle acceleration in reconnection layers is surprisingly robust despite the development of 3D turbulence and instabilities. We then study the large-scale reconnection acceleration by solving the Parker's transport equation in a background reconnecting flow provided by MHD simulations. Due to the compression effect, the simulations suggest fast particle acceleration to high energies in the reconnection layer. This study clarifies the nature of particle acceleration in reconnection layer, and may be important to understand particle acceleration and plasma energization during astrophysical high-energy flares in different settings.

I present recent work on particle resampling techniques designed to address certain scenarios in gyrokinetic PIC simulations: resampling particle sets to either reduce numerical noise or increase particle density in key simulation regions (e.g. the plasma edge or pedestal). We also consider downsampling and upsampling between different particle representations in multiscale simulations. The resampling is constructed to preserve key simulation observables, such as moments of the distribution function or charge deposition on the cell grid. The resampling algorithm is naturally low communication and straightforward to implement into an existing PIC software framework.

Plasmas are inherently multi-scale, with typical phenomena spanning over many orders of magnitude in both time and space. To computationally overcome this challenge, implicit (particle-in-cell) algorithms, such as the electromagnetic iPic3D code, have been developed, incorporating the kinetic behavior of plasma without losing track of the global evolution of the system. Next to magnetic reconnection-related topics, iPic3D has been especially designed to study the interaction with magnetized and non-magnetized bodies immersed in plasma. Over the last few years our computational efforts have led to significant advances to understand basic physics with direct impact on (future) space exploration. We identify and present the general mechanisms of the solar wind interaction with lunar magnetic anomalies and confirm the electrostatic formation of “minimagnetospheres” above the lunar surface. The latter is of particular interest, as we investigate a plasma environment where only the electron population is magnetized. We explore the interaction with various magnetic structures, including the Reiner Gamma region, and the effect of the upstream solar wind conditions. Finally, we investigate the role of lunar anomalies and the solar wind standoff for the formation of lunar swirls. This work opens new frontiers of research towards a deeper understanding of the kinetic interaction processes and is ideally suited to be compared with field or particle observations from spacecraft.

The interaction of lasers, plasmas, and particle beams presents a fascinating and vast parameter of space for exploration, innovation, and discovery that is rich with complex dynamics occurring over time scales and energy densities spanning many orders of magnitude. This line of research is interdisciplinary by nature, so it provides an excellent opportunity for shared knowledge and resources with other research groups at the university. It also tends to attract students due to the active hands-on nature of the experiments and the interesting potential future applications. These days, a laser-driven plasma wakefield accelerator system can easily fit within the lab space and budget of a university research program while performing cutting-edge research and exploring the fundamental physics of the highly non-linear beam-plasma interactions. In this talk I will outline an experimental research program that is centered around such a laser-beam-plasma system in the university lab, supplemented with collaborative research projects that would be conducted at one or more larger accelerator facilities around the world.

The key to progress in many unsolved mysteries in both space and fusion plasmas lies in improving our understanding of fundamental plasma physics processes. I will discuss two examples: magnetic reconnection and non-linear physics of Alfvén waves. 

From an arcade of magnetic flux loops on the surface of the sun to tokamak sawteeth, magnetic reconnection is not only fast, but also impulsive -- a slow buildup of magnetic energy is followed by a fast release. But the physics responsible for this is still an open question. Impulsive events observed in recent laboratory experiments [1-2] required 3-D physics to explain and exhibited features in common with events observed in the magnetosphere. Future work will include: 1) Satellite observations aimed at investigating events comparable to the experiment, and 2) Laboratory experiments on the new FLARE user facility at Princeton aimed at exploring a multi-X-line regime comparable to the magnetosphere.

Alfvén waves, a fundamental mode of magnetized plasmas, are ubiquitous in lab and space. The nonlinear behavior of these modes is thought to play a key role in important problems such as the heating of the solar corona, solar wind turbulence, and Alfvén eigenmodes in tokamaks. In particular, theoretical predictions show that these Alfvén waves may be unstable to various decay instabilities, even at very low amplitudes (δB/B<10-3), but this key physics has only recently been demonstrated for the first time in the laboratory [3-5]. My ongoing and future work aims to compare laboratory observations and satellite measurements in order to determine the regions of the heliosphere where Alfvén wave decay instabilities may play an important role. Proposed new projects include investigations of fundamental non-linear interaction physics using Alfvén eigenmodes in tokamak plasmas and whistler waves in a basic laboratory device.

The dynamic, nonlinear evolution of tearing instabilities on DIII-D reveals a coupling of multiple rotating magnetic island chains that enhances momentum transport. Islands of different toroidal mode number that exert no linear JxB force on one another couple nonlinearly to phase-lock, flattening the toroidal rotation profile. This behavior has been described by a model for 3-wave mixing similar to that evoked for the so-called ‘slinky’ mode observed in reversed field pinch devices, but as the edge safety factor is reduced toward values relevant to the ITER baseline, or 15 MA scenario, additional momentum transport and forces not encompassed by single fluid resistive MHD become dominant. These data are troubling in their implications for controlling rotation to optimize confinement and to reduce disruptivity in ITER, and they reveal critical shortcomings in our capability to model island-induced modifications of the neoclassical toroidal viscosity. However, the empirical results of this work are also encouraging in that they suggest new methods for the early detection of disruptive modes, such as real-time monitoring of the local effective Prandtl number. Microwave imaging diagnostics play a central role in executing these experiments and guiding the analysis that can lead to a deeper appreciation of the underlying physics.

As an Einstein Postdoctoral Fellow, I have focused my research towards fundamental High-Energy-Density (HED) plasma science relevant to supersonic plasma-jet dynamics in young stellar objects (YSOs). Astrophysical jets have been observed during all stages of low-mass star formation during the accretion process. While the genesis of these jets is still debated within the astrophysics community, our laboratory experiments focus on the dynamics of supersonic plasma flows in a background magnetic field where the dynamic plasma-beta is of order ~1-10, similar to the astrophysical case. I will discuss our two recent experimental campaigns and the current progress of data interpretation and simulation. This initial work led to my recent participation in the large Astrophysical Collisionless Shock Experiments with Lasers (ACSEL) collaboration where we are developing the means to create collisionless shocks in the laboratory. This type of shock is prevalent in many astrophysical systems and is crucial to the formation of supernova remnants. I will very briefly touch on this topic, as it is a new direction for my research and opens many opportunities for further study.

My present and future research interests lie in the astrophysical analogs of the HED systems that we create in the lab using high-power lasers. The fundamental plasma science at the heart of this field is essential to understanding some of the most interesting phenomena in our universe. In this field of research, large-scale physics experiments are often executed at user-facilities in the US and abroad, while much of the diagnostic and technological development is done at the academic institution. My research is motivated by outstanding questions in astrophysics, but the technologies developed for this work are of great importance to the whole HED physics community. I will briefly cover upcoming experiments at the Jupiter Laser Facility that will lay the ground work for future studies of shockprocessed dust-destruction rates in supernova remnants. I will also cover my plans to build a first class facility at CU Boulder for training students in the rapidly growing field of HED Laboratory Astrophysics.

The acceleration of high quality particle bunches to GeV energies has been experimentally demonstrated in plasma wakefield accelerators, using either strong laser pulses (Laser-driven Wakefield Acceleartors or LWFA) or highly relativistic particle beams (PWFA) as wakefield drivers. However, the quality of the bunches has not yet been comparable to what is reached in ordinary RF-based accelerators, making it challenging to apply plasma accelerators to end-use applications like free electron lasers (FEL). The underdense photocathode injection method (Trojan Horse method) in Plasma Wakefield Accelerators (PWFA) promises to produce high quality electron bunches capable of running (for example) FELs. The Trojan Horse method introduces the need for a highly relativistic electron beam itself, and currently the only facility that provides sufficient high charge and energy drive beams is FACET. To overcome this lack of suitable drivers, the use of a laser wakefield accelerator is promising. The production and acceleration of the witness bunch in the PWFA stage is stable under variation of the drive beam quality to a certain extent. Additionally, the requirements on the quality of the LWFA output are significantly reduced compared to end applications like FELs.

In a series of experiments, magnetic flux ropes as well as long and narrow current sheets are generated in a background magnetoplasma capable of supporting Alfvén waves. The flux ropes are kink unstable and smash into one another as they move. When they do, reconnection events occur. The current sheet rapidly tears into a series of magnetic islands when viewed in a cross-sectional plane, but are three-dimensional flux ropes. At the onset of the current, magnetic field line reconnection is observed between the flux ropes. The sheet on the whole is kink unstable, and after kinking exhibits large scale, low frequency (f≪fci) rotation about the background field with an amplitude that grows with distance from the source of the current. Three-dimensional data (at up to 50,000 spatial locations and thousands of time steps) of the magnetic and total electric field is acquired throughout the duration of the two experiments and the parallel resistivity is derived from it. The parallel resistivity, for the most part, is not largest in the reconnection regions; rather it peaks in the neighborhood of the current gradient. Quasi-separatrix layers - regions in which magnetic field lined rapidly diverge - are observed in both cases. The dynamics of multiple ropes is similar to that of the ropes that the current sheet tears into. The permutation entropy is calculated from time series of the magnetic field or flow data and used to calculate the Jensen Shannon complexity map. The location of data on this map indicates if the magnetic fields are stochastic, or chaotic. The complexity is a function of space and time. The entropy and complexity change in space and time, which reflects the change, and possibly type, of chaos associated with the ropes. The maps give insight as to the type of chaos (deterministic chaos, fractional diffusion, Levi flights...) and underlying dynamical process. The power spectra of much of the magnetic field and flow data is exponential and Lorentzian structures in the time domain are embedded within them.

Solar flares produce non-thermal electrons with energies up to tens of MeVs. To understand the origin of energetic electrons, coronal hard X-ray (HXR) sources, in particular above-the-looptop sources, have been studied extensively. However, it still remains unclear how energies are partitioned between thermal and non-thermal electrons within the above-the-looptop source. Here we show that the kappa distribution, when compared to conventional spectral models, can better characterize the above-the-looptop HXRs (>~ 15 keV) observed in four different cases. Based on the kappa distribution model, we found that the 2012 July 19 flare showed the largest non-thermal fraction of electron energies about 50%, suggesting equipartition of energies. Considering the results of particle-in-cell simulations, as well as density estimates of the four cases studied, we propose a scenario in which electron acceleration is achieved primarily by collisionless magnetic reconnection, but the electron energy partition in the above-the-looptop source depends on the source density. In low-density above-the-looptop regions (few times 10^9 cm^-3 ), the enhanced non-thermal tail can remain and a prominent HXR source is created, whereas in higher densities (>10^10 cm^-3), the non-thermal tail is suppressed or thermalized by Coulomb collisions.

Nonlinear energy fluxes are known to redistribute the energies according to the detailed conservation laws. For example, the energy produced in the linearly unstable plasma is transported by the nonlinear flux toward larger or smaller scales where it is dissipated by the viscosity. As such a role is crucial in sustaining a steady state, most analyses on the flux focus in terms of the transport. Yet, there is another side of the nonlinear flux altering the temporal response of the plasma from the linear reaction. In this seminar the features of this part of the flux, to be called in the presentation as non-transporting flux (NTF), are highlighted in the context of the electrostatic resistive-drift fluid turbulence. Simulations are performed for three cases of adiabaticity parameter of the Hasegawa-Wakatani model. When the zonal flow is not present, the time scales of the energy-transporting flux and the NTF are of the same order. The energy NTF is found to be anisotropic and advective in the sense that it is approximately proportional to the gradient of the energy in the direction of the Fourier space with the proportionality coefficient being dimensionally advecting velocity. When the zonal flow is allowed to be excited, the time scale of the NTF becomes much shorter than that of the energy- redistributing flux as the plasma comes to be adiabatic where the zonal part of the energy is much larger than the non-zonal counterpart. Details will be discussed at the presentation.

No Abstract Available

We consider dynamics and turbulent interaction of whistler modes within the framework of inertialess electron MHD (EMHD). We argue there is no energy principle in EMHD: any stationary closed configuration is neutrally stable.

We derive the Hamiltonian formulation of EMHD in a canonical form; we calculate the matrix elements for the three-wave interaction of whistlers and show that (i) harmonic whistlers are exact non-linear solutions; (ii) co-linear whistlers do not interact (including counter- propagating); (iii) whistler modes have a dispersion that allows a three-wave decay, including into a zero frequency mode; (iv) the three-wave interaction effectively couples modes with highly different wave numbers and propagation angles.

We solve numerically the kinetic equation and show that, generally, the EMHD cascade is non-univeral - it depends on the forcing and often fails to reach a steady state. Analytical estimates predict the spectrum of magnetic fluctuations for the quasi-isotropic cascade ~ k^?2. The cascade remains weak (not critically- balanced). The cascade is UV-local, while the infrared locality is weakly (logarithmically) violated.

Fluctuations in magnetized laboratory plasmas are ubiquitous and complex. In addition to deleterious effects, like increasing heat and particle transport in magnetic fusion energy devices, fluctuations also provide a diagnostic opportunity. Identification of a fluctuation with a particular wave or instability gives detailed information about the properties of the underlying plasma. In this work, diagnostics and spectral analysis techniques for fluctuations are developed and applied to two different laboratory plasma experiments.

Spectral properties of coherent waves in an argon plasma column are examined using fluctuation data from fast imaging. Experimental dispersion relation estimates are constructed from imaging data alone using a cross-spectral-density technique. Electron drift waves are identified by comparison with theoretical dispersion curves, and a tentative match of a low-frequency spectral feature to Kelvin-Helmholtz-driven waves is presented.

Transient fluctuations are examined in a local spheromak merging experiment using a multi-channel magnetic probe. A histogram cross-spectral analysis technique allows experimental dispersion relation estimates to be made from magnetic measurements. Hints of waves in the range of ion-cyclotron frequency harmonics are observed in conjunction with merging events.

Magentohydrodynamic (MHD) instabilities with poloidal and toroidal harmonics m=1 and n=1 have been a paradigm for the study of toroidal effects in magnetically confined fusion plasmas. The linear perturbation theory of the 1/1 internal kink has demonstrated the fundamental importance of toroidal mode coupling to poloidal harmonics m=2,0 and higher at n=1 for incompressible and compressible modes. Nonlinear MHD simulations of the resistive internal kink and sawtooth crash routinely include compressibility and mode coupling, but most analysis has been limited to reduced MHD (RMHD), which drops both effects. A new approach shows that compressible and toroidal effects at low resistivity can be analyzed in terms of the perpendicular momentum equation, with consequences that are quite different from RMHD. MHD at low resistivity allows a fast sawtooth crash in a torus that resembles many features observed in experiments. Related effects appear in other common instabilities, such as magnetic islands and edge modes. A separate density evolution also allows the nonlinear existence of long-lived 1/1 helical ion density snakes around q=1, even in the presence of periodic sawtooth crashes, as observed in many experiments.

The Crab Nebula is considered as the high-energy astrophysical source par excellence, and as an ideal laboratory for particle acceleration in relativistic magnetized plasmas of pairs. Yet, the recent discovery of intense gamma-ray flares from the Crab Nebula does not fit into the traditional picture of pulsar wind nebulae. I will argue that the origin of the flares may lie in sudden episodes of magnetic dissipation within the nebula via magnetic reconnection. This scenario is corroborated by particle-in-cell (PIC) simulations of ultra-relativistic pair plasma reconnection subject to strong synchrotron cooling. I will discuss the conditions under which particle acceleration is most efficient, focusing on new large-scale three-dimensional PIC simulations.

Particle transport in plasmas with turbulent magnetic fields in the presence of a gradient of the mean magnetic field and weak pitch-angle diffusion is analyzed. We demonstrate that such transport is described by asymmetric diffusion: the generalization of the conventional random walk process to the case of unequal transition probabilities. We construct a toy 1D Markov chain model and analytically demonstrate that the particle density distribution becomes exponential in distance, instead of linear as is the case of the standard diffusion process. Implication of our results for the transport of cosmic rays are discussed.

I will present results of the first self-consistent reacting multi-fluid simulations of magnetic reconnection in a partially ionized plasma, where the ionized and neutral fluids are treated as coupled but distinct. Partially ionized plasma environments, where release of magnetic energy and topological reconfiguration of magnetic fields via magnetic reconnection is known or conjectured to take, place range from highly collisional, e.g. interstellar medium and lower solar chromosphere with ionization fraction below 0.1%, to weakly collisional, e.g. in the upper solar chromosphere with ionization fraction of 1%-10%. Different plasma processes, such as ionization and recombination, ion neutral interaction via charge-exchange collisions, Hall currents, and radiative losses can become the dominant factors in determining the reconnection rate and the structure of the reconnection region in different parameter regimes. The HiFi multi-fluid modeling framework has been used to implement all of the above processes in a single self-consistent model and to perform 2D simulations of magnetic reconnection under a variety of plasma conditions. In particular, as shown in the adjacent image, we observe the formation of previously predicted non-LTE current layers and explore the associated onset of the secondary plasmoid instability.

No Abstract Available

Flux ropes form basic building blocks for magnetic dynamics, are analogues of macroscopic magnetic field lines, and are irreducibly three dimensional (3D).

We have used the Reconnection Scaling Experiment (RSX) to study flux ropes, and have found many new features involving unexpected 3D dynamics, kink instability driven reconnection, non linearly stable but kinking flux ropes, large flows, and shear flow induced magnetic fields. For example the onset threshold for external kink instability depends upon boundary conditions that can be adjusted between line tied and free. These two boundary conditions could correspond to CME eruption flux ropes that are anchored ("line tied") at one end to solar coronal holes while the other end remains "free" to drift as magnetic clouds in the solar system. The dynamics of two flux ropes form a fairly simple 3D system that allowed the first identification of how a plasma instability (in this case the kink) initiated magnetic reconnection. When there is significant guide magnetic field, flux ropes bounce off each other much of the time instead of merging and reconnecting. As we assemble large 3D experimental data sets for density, temperature, pressure, magnetic field, and current density we observe local violations of MHD, and strongly sheared flow and fields. We show data where magnetic field is generated from sheared electron fluid flow. Movies from 3D experimental data also show that MHD forces fail to balance, i.e. JxB - grad P_e does not vanish at the 30% level, and we evaluate some candidates for the missing physics. We intend to model these 3D data with a PIC code (VPIC), 2 fluid code (HiFi) and possibly other hybrid approaches, and solicit collaborators.

*DOE Fusion Energy Sciences DE-AC52-06NA25396, NASA Geospace NNHIOA044I, Basic

Magnetic reconnection transforms magnetic field energy into particle kinetic energy; it may be the mechanism for accelerating particles to high enough energies to emit energetic synchrotron radiation, which is observed in various astrophysical objects, including pulsars, active Galactic nuclei, and gamma-ray bursts. Using 2D particle-in-cell simulations of relativistic, radiating, pair plasma reconnection, this work demonstrates that reconnection accelerates particles, bunching and focusing the most energetic particles into a narrow beam that wiggles in the plane of the reconnection layer. This beaming leads to brief, intense flares of high-energy photons when the beam crosses the line of sight. A newly-developed PIC code, which includes the radiation reaction, has recently shed new light (so to speak) on the picture of relativistic reconnection under strong synchrotron cooling. The most energetic particles feel very little radiative losses while they are accelerated in a straight line deep inside the layer where the electric field exceeds the magnetic field. Eventually, the particles get kicked out of the layer and subsequently radiate >160 MeV synchrotron radiation, which would be impossible to explain with ideal MHD-based models of particle acceleration. This result is essential in understanding the origin of >100 MeV gamma-ray flares observed in the Crab Nebula.

Recent advances in imaging present tantalizing prospects for diagnosing fluctuations in laboratory plasmas. Commercially available cameras now allow recording of large arrays of simultaneous data points on relevant time scales. In this talk, I will present the status of our ongoing study of imaging-based plasma turbulence measurements in the Controlled Shear Decorrelation Experiment (CSDX) at the University of California, San Diego. CSDX is a linear machine producing dense plasmas relevant to the tokamak edge (T_e ~ 3 eV, n_e ~ 10^13/cc). Electrostatic fluctuations are measured with Langmuir probes in concert with visible-light imaging over a range of plasma parameters. Comparisons between probe and imaging data constrain operational limits for both diagnostics. Drift like modes are observed and characterized using an image correlation technique. Time-resolved velocity fields are obtained using a pattern-matching algorithm, allowing access to flow dynamics across the plasma radius. Current work includes measurements of wave dispersion, velocity profiles, and probe/imaging relationships.

No Abstract Available

Global electromagnetic gyrokinetic simulations show the existence of near threshold conditions, for both a high-n Kinetic Ballooning Mode (KBM) and an intermediate-n kinetic version of Peeling-Ballooning Mode (PBM). The KBM and the PBM have been used to constrain the EPED model [1]. Global gyrokinetic simulations show that the H-mode pedestal, just prior to the onset of the Edge Localized Mode (ELM), is very near the KBM threshold. Two DIII-D experimental discharges are studied, one reporting KBM features in fluctuation measurements [2]. Simulations find that in addition to the high-n KBM, an intermediate-n electromagnetic mode is unstable. This kinetic version of the PBM has phase velocity in the electron diamagnetic direction, but otherwise has features similar to the MHD PBM. When the magnetic shear is reduced in a narrow region near the steep pressure gradient, the intermediate-n kinetic PBM'' is stabilized, while the high-n KBM becomes the most unstable mode. Global simulation results of the KBM compare favorably with flux tube simulations. The KBM transitions to an unstable electrostatic ion mode as the plasma beta is reduced. The intermediate-n "kinetic peeling ballooning mode'' is sensitive to the q-profile and only seen in global electromagnetic simulations. Collisions increase the KBM critical beta and growth rate. These results indicate that an improved pedestal model should include, in detail, any corrections to the bootstrap current, and any other equilibrium effects that might reduce the local magnetic shear. The bootstrap current may flatten the q-profile in the steep gradient region[3]. Simulations are carried out using the global electromagnetic GEM code, including kinetic electrons, electron-ion collisions and the effects of realistic magnetic geometry, including the MHD kink term. In addition to global linear analysis, nonlinear simulations will be reported showing that, while the equilibrium radial electric field has a weak effect on the linear growth rate, it has a larger stabilizing effect nonlinearly.

[1] P. Snyder, et al., Phys. Plasmas 16 056118 (2009).

[2] Z. Yan, et al., Phys. Plasmas 18 056117 (2011).

[3] J. Callen, et al. Nucl. Fusion 50 064004 (2010).

A plasma in which the inter-particle spacing approaches the thermal de Broglie wavelength must be subject to statistical effects due to Pauli exclusion. Also, many familiar plasma phenomena could be modified on such length scales because of the Heisenberg uncertainty principle. The question of how to model quantum effects in plasmas pushes the envelope of our knowledge of plasma physics and applies the well-established principles of quantum mechanics in a novel context. We will discuss potential quantum effects in plasmas and the possibility of real systems exhibiting these effects, followed by an overview of how to model such plasmas. In addition, a mean-field quantum kinetic model will be applied to the case of unmagnetized Fermi-Dirac equilibrium plasmas with arbitrary degree of degeneracy. Linear dispersion relations for electrostatic waves, including Landau damping, will be derived and analyzed. We will conclude with a discussion of possible future directions within this area of research.

The physics capabilities of modern gyrokinetic microstability codes, e.g. GEM, GYRO, and GS2, are now so extensive that they can be expected to predict energy and particle transport in tokamaks. Therefore, they are being validated by comparing their results with transport measurements in existing devices. However, as a prerequisite, they must be verified, i.e., demonstrate that they correctly solve the underlying gyrokinetic-Maxwell equations. Because of the complexity of actual tokamak plasmas, this cannot be accomplished using purely analytic approaches. Instead, verification must rely on benchmarking (comparing different code results for identical plasmas and physics) - the premise being that all the codes would not produce the same erroneous results. We will present benchmarking exercises for a low-power DIII-D discharge and a high-power Alcator C-Mod discharge at the mid-radius of the plasma, both omitting and including equilibrium ExB flow shear. This benchmarking includes magnetic fluctuations, plasma shaping, kinetic electrons, collisions, and one impurity. In addition, we compare linear results among the three codes for the steep-gradient edge region of a DIII-D plasma. These three disparate plasmas and radial locations serve to test the codes over a broad range of plasma parameters.

The turbulent cross helicity (velocity--magnetic-field correlation in turbulence) coupled with the large-scale vortical motion leads to the turbulent electromotive force aligned with the mean vortical motion. This is called the cross-helicity effect in magnetic-field induction, and is in remarkable contrast with the well-known helicity or alpha effect, where the induced electromotive force is aligned with the mean magnetic field. The cross-helicity effects have been investigated in several astro/geophysical and fusion plasma phenomena. Some interesting features of the cross-helicity effects will be presented with special reference to the turbulent magnetic reconnection. It is stressed that the combination of the transport enhancement and suppression due to turbulence plays an important role in magnetic reconnection.

Reconnection is a process of intense localised phenomena. Particularly active are the regions of transition between fresh plasma with unreconnected field lines and processed plasma embedded in reconnected field lines. These regions are characterised by a plurality of possible drivers of instability: flows, shears, anisotropies. We will review the results obtained by the MMS theory team at colorado in collaboration with the center of plasma astrophysics (CPA) at the KU Leuven in Belgium. We will identify several instances of waves and instabilities measured in simulations and try to discuss possible causes. The format will be truly seminarial, open to discussion and suggestion from the attendees.

Surfaces of airless bodies and spacecraft in space are exposed to a variety of charging environments such that a balance of plasma determines the surface charge. Photoelectron emission due to intense solar UV radiation is the dominant charging process on sunlit surfaces, and to first order this results in a positive surface potential, with a photoelectron sheath immediately above the surface. Due to experimental constraints, little laboratory work has been done to characterize this type of plasma. I will present the results of Langmuir probe measurements above both conducting and insulating surfaces in vacuum, and compare some of these measurements with the results from 1D PIC-code simulations to gain a greater understanding of the sheath physics.

No Abstract Available

The four-satellite Magnetospheric MultiScale (MMS) mission, scheduled for launch in 2014, will be able to measure full 3D electron velocity distributions over time intervals as short as 30ms. MMS therefore has the potential of resolving distributions associated with magnetic reconnection in Earth's magnetotail that are effectively local (i.e., for which the motion of the reconnection environment relative to the satellite can be neglected to lowest order). In this talk, I will present the results of implicit-PIC simulations of magnetotail reconnection, with the focus on electron dynamics near the x-point and along branches of the magnetic separatrix. In addition to electron velocity distributions averaged over times resolvable by MMS, the trajectories of selected sets of tagged simulation particles will be presented. These trajectories provide insights into the origin of nonthermal features in the velocity distributions, including the bimodal signatures of (saturated) streaming instabilities that produce electron phase-space holes near the separatrix. Bipolar electric-fields associated with electron holes have been previously observed (e.g., by Cluster) in the vicinity of magnetotail reconnection.

No Abstract Available

Equilibrium reconstruction is the process of inferring the parameters characterizing an MHD equilibrium from experimental observations. It is used extensively for axisymmetric plasmas such as those in tokamaks and reversed field pinches, and is the primary basis for reconciling measurements, and assessing plasma stability and transport. For non-axisymmetric plasmas, such as those in stellarators and quasi-helical states of reversed-field pinches, standard axisymmetric equilibrium reconstruction codes based on the Grad-Shafranov equation are inadequate. I will report on progress and results from the V3FIT non-axisymmetric equilibrium reconstruction code.

No Abstract Available

I will discuss drift and Hall effects on tearing modes, island evolution, and relaxation in pinch configurations. An unexpected new result is a drift effect that reduces the growth rate of the tearing mode where the drift is proportional to gradB and poloidal curvature [King et al., Phys. Pl. 2011]. Although computations with the NIMROD code use a non-reduced fluid model, analytics with tearing ordering show this drift is manifest through contributions from ion gyroviscosity. Nonlinear single helicity computations with experimentally-relevant parameters show that the warm-ion gyroviscous effects reduce saturated island widths. In contrast to diamagnetic drift-tearing where the associated pressure-profile gradient is flattened nonlinearly, the gradB and poloidal-curvature profiles are largely unaffected by magnetic islands.

Computations with multiple modes similar to reversed-field pinch discharges show that both MHD and Hall dynamos contribute to relaxation events. The presence of Hall dynamo implies a fluctuation-induced Maxwell stress, and the simulation results show net transport of parallel momentum. The magnitude of force densities from the Maxwell stress and a competing Reynolds stress, and changes in the parallel flow profile are within a factor of 1.5 of measurements [Kuritsyn et al., Phys. Pl. 2009] during a relaxation event in the Madison Symmetric Torus.

The Crab Nebula was formed after the collapse of a star recorded by Chinese astronomers in 1054 AD. The nebula is filled with relativistic electron-positron pairs injected by a powerful pulsar, and radiates at all wavelengths, from radio to very-high energy gamma rays. The gamma-ray space telescopes Agile and Fermi recently detected bright day-long flares above 100 MeV energy photons, presumably of synchrotron origin. This discovery implies that electrons and positrons are accelerated to PeV energies in the nebula, the highest energy particles ever attributed to a specific astrophysical object. The existence of these particles challenges the most established models of particle acceleration. In this talk, I will argue that the flares could be powered by magnetic reconnection in the nebula. Relativistic test-particle simulations show that the particles are naturally focused into a thin fan beam, and accelerated deep inside the reconnection layer. I will show that this scenario provides a viable explanation for the gamma-ray flares in the Crab Nebula.

At the Colorado Center for Lunar Dust and Atmospheric Studies, we are building a 3MV dust accelerator to study dusty plasmas which occur naturally on the lunar surface. Dust accelerators are an important research tool that can be used to study many impact phenomena (i.e., impact generated plasma, ejecta composition), as well as to test instruments that have to withstand the harsh environment of outer space. I will present a summary of science that can be done with a dust accelerator, as well as the tools that can be developed using a dust accelerator, and then discuss the design and performance of the accelerator currently being built here at the University of Colorado.

Spontaneous rapid growth of strong magnetic fields is rather ubiquitous in high-energy density environments ranging from laser-plasma interaction laboratory experiments, to reconnection and astrophysical objects, where they are produced by kinetic streaming instabilities of the Weibel type. In the talk, we will discuss spectral and temporal properties of radiation emitted by relativistic electrons in the course of the Weibel instability development and saturation. In our study we consider (i) anisotropic magnetic fields and electron velocity distributions, (ii) the effects of trapped electrons and (iii) extends the description to large deflection angles of radiating particles thus establishing a cross-over between the classical jitter and synchrotron regimes. The analytical and numerical results obtained from particle-in-cell simulations of the classical Weibel instability will be presented. Radiation emitted has a markedly non-synchrotron spectral energy distribution, which can be use as a benchmark of the sub-Larmor-scale magnetic fields in the system.

No Abstract Available

Neoclassical tearing modes (NTMs), which degrade plasma confinement and may also trigger disruptions in toroidal plasmas, have successfully been suppressed or controlled in many experiments by the local application of electron cyclotron current drive (ECCD) in or near the magnetic island formed by the NTM. The development of integrated, predictive models to determine optimal strategies for stabilizing these modes in ITER is a subject of ongoing interest. The Integrated Plasma Simulator (IPS) framework, developed by the SWIM Project Team, facilitates self-consistent simulations of complicated plasma behavior via the coupling of various codes modeling different spatial and temporal scales in the plasma. Here, we apply this capability to investigate the stabilization of tearing modes by ECCD. Under IPS control, the NIMROD code (MHD) evolves fluid equations to model bulk plasma behavior, while the GENRAY code (RF) calculates the self-consistent propagation and deposition of RF power in the resulting plasma profiles. GENRAY data processed by the qhull (computational geometry) software package is then used to construct moments of the quasilinear diffusion tensor (induced by the RF); these moments in turn influence the dynamics of current/momentum/energy evolution in NIMROD's equations. We present initial results from these coupled simulations and demonstrate that they correctly capture the physics of magnetic island stabilization [T. G. Jenkins et al., Phys. Plasmas 17, 012502 (2010)] in the low-beta limit. An overview of ongoing model development (synthetic diagnostics and plasma control systems; neoclassical effects; etc.) is also presented.

Langmuir waves are electrostatic waves near the plasma frequency that can be generated by beam-unstable electron distributions and can be converted into electromagnetic radiation at the plasma frequency and its harmonic. These waves exist in a variety of heliospheric contexts whenever strong electron beams are present (eg. solar flares, traveling shock fronts, planetary bow shocks, auroral regions). Through measurement of remotely generated radiation and in-situ waveforms, Langmuir waves are integral to the study of solar flares, the heliospheric density profile, coronal mass ejections, planetary bow shocks, auroral processes, and plasma turbulence. We focus on this final application, presenting observations and modeling of the interactions between Langmuir waves and density fluctuations in the turbulent solar wind at 1 AU. We focus on how density turbulence may be studied through its effects on Langmuir wave localization, electric field amplitude distributions, and expression of wave dimensionality. 

In this talk I will discuss the dust charging calculation based on the Orbital Motion Limited theory (Mott-Smith and Langmuir, 1926). The charging state of dust particles in a plasma depends on the dust properties as well as the environment. The dust equilibrium potential can be derived by considering the balance of various charging currents, including the collection of electrons/ions from the ambient plasma and the emission of secondary electrons and photoelectrons. Other processes such as the field emission, the electrostatic disruption (i.e., coulomb explosion), and the stochastic charging behavior will be briefly discussed. I will also present few examples to demonstrate the role of varying charging state in the evolution of dust dynamics.

In magnetic fusion devices, turbulence is known to drive transport of particles and heat leading to degraded confinement. This anomalous transport is a primary performance limitation in these devices, and the fusion capability of current and future devices will depend on the ability to suppress this turbulent transport. Recent theoretical predictions and experimental results suggest that the turbulence interacts with mesoscale flows, or zonal flows, and shearing of these flows can lead to suppression of turbulence. In the talk, I will present results from the Gas Puff Imaging (GPI) diagnostic on the National Spherical Torus Experiment (NSTX). Low-High confinement mode transition experiments revealed, for the first time on NSTX, a periodic modulation of the edge turbulence amplitude in L-mode plasmas. These modulations were marked by a reduction in plasma being ejected into the Scrape-off layer, and a quiescent, H-mode like edge. These 'quiet period' oscillations and the correlations with edge flow parameters will be discussed. In addition, recent evidence of zonal flows in the NSTX edge, as diagnosed by the GPI diagnostic, will be presented along with analysis of turbulent flow properties, including the shearing rate and Reynolds stress.

Eruptive flares and coronal mass ejections (CMEs) are believed to correspond to a sudden, explosive release of the free magnetic energy stored in the previously quasi-equilibrium, twisted/sheared coronal magnetic fields. However, the detailed magnetic field structure for the eruption precursors and the physical causes for their sudden disruption remain fundamental unanswered questions under investigation. I present three-dimensional MHD simulations of the evolution of the magnetic field in the corona where the emergence of a twisted magnetic flux rope is driven at the lower boundary into a pre-existing coronal potential arcade field. Through a sequence of simulations in which a varying amount of twisted flux is transported into the corona before the emergence is stopped, I investigate the conditions that lead to a dynamic eruption of the resulting coronal flux rope. It is found that the eruption is triggered when the flux rope in the corona rises to a critical height where the corresponding potential field declines with height at a sufficiently steep rate, a mechanism consistent with the onset of the torus instability. The simulations suggest that S (or inverse S) shaped current sheets develop under the flux rope during the quasi-static phase before the eruption, and reconnections in the current sheet effectively reduce the anchoring of the flux rope, allowing it to rise quasi-statically to the critical height, and the dynamic eruption ensues. Through tracing reconnected field lines during the eruption, the evolution and morphology of the X-ray post-flare loops and their foot-points corresponding to the flare ribbons are deduced, which reproduce some of the commonly observed features associated with eruptive flares in regions with pre-existing X-ray sigmoids. I also present preliminary results from MHD simulations that model qualitatively the magnetic field evolution of the eruptive flare occurred on December 13, 2006 in the emerging delta-sunspot region NOAA 10930 observed by the Hinode satellite.

We present the first joint electron and ion velocity observations from solar wind reconnection exhausts as recorded by TH-C in 2009-2010. The MVAB method is used to find the reference frame of the exhaust where L and N correspond to eigenvectors of maximum and minimum field variance, and M=NxL. Many cases (60) now confirm for the first time that the electrons match the measured ion velocity signature along the jet direction (VL) in the solar wind rest frame of the exhaust. This is expected within exhaust channels where ions and electrons are predicted to move together at the ExB drift. We also present examples where electrons move faster than ions (VLe>VLi) at both exhaust edges. Initial results suggest that a majority of events do not display electrons moving toward the X-line at the exhaust edges. This feature is either too thin to be resolved by the 3-s (1200 km at 400 km/s solar wind) instrument resolution or else is only present closer to the X-line consistent with a general lack of Hall magnetic field signatures at solar wind exhausts. Ions and electrons are generally consistent with the predicted V=V0+/-dV velocity at the two correlated (+dV) and anti-correlated (-dV) exhaust edges. V0 is an external reference velocity and dV is derived from the Walen relation based on electron density and proton mass [Paschmann et al., 1986]. However, we show a case where ions and electrons seemed to follow separate +/- branches of the predicted Walen relation on one side of an exhaust. The electrons (ions) displayed a negative (positive) correlation between VL and BL when a positive correlation was expected for both. This event and cases of faster electron than ion speeds at both exhaust edges suggest that the two species may display separate turn-over points of the VL-BL phase transition within exhausts.

No Abstract Available

Astrophysical bodies -- planets, stars, and galaxies -- have their own dynamos that generate, maintain, and evolve their magnetic fields. Best known to us are the dynamos of the Earth's interior and the Sun. These have certain common features, such as magnetic polarity reversals, but they operate in very different physical regimes. The geodynamo operates in a fully nonlinear magnetohydrodynamic regime in which primarily the magnetic fields govern the dynamics, while the Sun works primarily in a hydrodynamical regime. That is, the Sun's global differential rotation, meridional circulation and some smaller scale turbulent motions provide dynamo action, and the back-reaction from induced magnetic fields affects them relatively little. This difference means that a kinematic 'mean-field' approach to the solar dynamo can be very successful, but won't work for the geodynamo.

Over the past half-century, solar dynamo theory has proceeded along two parallel tracks: axisymmetric mean-field models, particularly the so-called 'flux-transport' models, and full 3D MHD models. Breakthroughs using mean-field models include explaining the solar cycle period, how the fields reverse, and what features can be predicted. Full 3D MHD models now produce cyclic evolution of the fields. I will review recent developments for both model types.

The biggest remaining challenge is how to include the effects of unresolved small scale processes, such as the rising of magnetic flux-tubes and MHD turbulence. Current full 3D MHD models are themselves mean-field models -- very sophisticated, but very expensive -- that are very hard to use to advance our understanding of the solar dynamo. But axisymmetric kinematic flux-transport models also have limitations. There is a third class of model, intermediate in complexity and expense, that offers the opportunity to extend our understanding of the solar cycle by explaining global departures from axisymmetry, such as 'active longitudes', 'sector boundaries', and 'tilted dipole' structures. I will describe how this model can be built as a generalization of axisymmetric flux transport dynamo models.

Transport in tokamaks is anomalous, caused by small scale plasma turbulence. Particle-in-Cell simulations have been the primary tool for studying micro-turbulence and predicting the anomalous transport level in future devices such as ITER. Many people believe that now is the time for pushing for truly first principle simulations of tokamak plasmas on the transport time scale, thanks to the development of the gyrokinetic model and the delta-f method, and supercomputers with tens of thousands of processors. In this talk I will describe the status of a gyrokinetic delta-f PIC code GEM, explain the unique algorithm used in GEM that solves numerical difficulties arising from the fast electron motion along the magnetic field, and present future plans for GEM development. I will discuss what I perceive to be the most important challenges to a transport time scale simulation, namely (1) the difficulty with determining long wavelength radial electric field in gyrokinetics and (2) lack of scale separation in a global simulation. I will speculate on ways to solve these challenging problems.

Reconnection is a key process in laboratory and astrophysics, it converts vast amounts of magnetic energy into kinetic energy, efficiently and fast. The spectacular events of reconnection, in solar flares, in geomagnetic storms, in the jets from supermassive black holes are just examples of sites where tremendous energies are converted into relativistic particles and heat. The community has been faced for decades to explain why this is possible. According to standard macroscopic theory, reconnection should be slow. To name an example, a solar flare should last decades not minutes. A vast gulf of several orders of magnitude separate our understanding from reality. Recently, great advances have been made by going beyond macroscopic theory to include kinetic scale events. The fascinating discovery is that kinetic scales do not simply act as turbulent noise akin to collisions, as it had always been imagined. Rather, kinetic effects change profoundly the system at large scales. Here we focus on one type of processes, the instabilities due to drifts in the region of reconnection: lower hybrid drift instability, Buneman instability and anisotropy-driven instabilities.

1. G. Lapenta, J.U. Brackbill, Nonlinear Evolution of the Lower Hybrid Drift Instability: Current Sheet Thinning and Kinking, Physics of Plasmas, 9, 1544-1554, 2002.
2. P. Ricci, J.U. Brackbill, W.S. Daughton, G. Lapenta, Influence of the Lower-Hybrid Drift Instability on the onset of Magnetic Reconnection, Physics of Plasmas, 11, 4489-4500, 2004.
3. W. Daughton, G. Lapenta, P. Ricci, Nonlinear Evolution of the Lower-hybrid Drift Instability in a Current Sheet, Physical Review Letters, 93, 105004, 2004.
4. G. Lapenta, J. King, Study of Current Intensification by Compression in the Earth Magnetotail, Journal of Geophysical Research, 112, A12204, doi:10.1029/2007JA012527, 2007.
5. G. Lapenta, Large scale momentum exchange by microinstabilities: a process happening in laboratory and space plasmas, Physica Scripta, 80, 035507, 2009.

The dissipation mechanism that breaks magnetic field lines during reconnection has remained a mystery since the first models of reconnection were proposed in the 1950s. Classical resistivity is too small to explain reconnection observations in tokamak sawteeth, the solar corona and heliosphere. 3-D particle-in-cell simulations of magnetic reconnection reveal that strong currents and associated high electron-ion streaming velocities that develop near the x-line can drive instabilities. The electron scattering caused by this turbulence produces an enhanced drag, "anomalous resistivity", that has been widely invoked as the dissipation mechanism. We have demonstrated with simulations and analytic modeling that during low-beta reconnection with a guide field that electron current layers become strongly turbulent. The surprise, however, is that the turbulence driven by an electron sheared-flow instability completely dominates traditional streaming instabilities and the associated turbulent driven strong transverse momentum transport, dubbed "anomalous viscosity", balances the reconnection electric field and therefore breaks field lines. The turbulence modestly enhances the rate of reconnection. This instability was not seen in earlier simulations because of the limited scale size of earlier computational domains. The instability is electromagnetic, is part of the whistler branch and therefore falls below the electron cyclotron frequency. The ions play no significant role. A second surprise is that a guide field is required for the instability to exist so that reconnection with a guide field exhibits stronger turbulence than anti-parallel reconnection. Signatures of this turbulence that could be explored in laboratory reconnection experiments and satellite observations are discussed.

A natural fueling mechanism that helps to maintain the main core deuterium and tritium (DT) density profiles in a tokamak fusion reactor is presented. In H-mode plasmas dominated by ion-temperature gradient (ITG) driven turbulence, cold DT ions near the edge will naturally pinch radially inward towards the core. The mechanism is investigated using the gyrokinetic turbulence code GEM and is analyzed using quasilinear theory. At the edge, this pinch effect of cold ions could help to explain the pedestal density buildup. Recent DEGAS 2 calculations indicate the neutrals in the pedestal are colder than the background ions. We have shown that near to the pedestal top the pinch flow velocity of recycling ion source is significantly higher than that of the outgoing main ions, and is dependent on its cold temperature.

The behavior of expanding dense plasmas has long been a topic of interest in space plasma research, particularly in the case of expansion within a magnetized background plasma. Expansion perpendicular to B causes a wide range of effects, including a 'diamagnetic bubble' or localized reduction of the background field, as well as visible periodic structures on the expanding plasma surface. A recent series of experiments at the UCLA Large Plasma Device (LaPD) studied these phenomena via a laser-produced plasma immersed in a large magnetized background plasma. The structure of the expanding plasma is diagnosed in three dimensions via a high-resolution in-plasma probe drive. Currents within the expanding plasma are found to have complex structure in three dimensions; in particular, an unexpected current system along the background field was discovered at the cavity surface. In addition to measurement of the plasma structure, the time behavior of large-scale periodic structures on the plasma surface was investigated via two-probe correlation analysis, revealing that the structures are static and translate with the bubble across the background field.

Wind and Cluster spacecraft observations of reconnecting current sheets in the Earth`s magnetotail show strong electron temperature anisotropy. This anisotropy is accounted for in a solution of the Vlasov equation that was recently derived for general reconnection geometries with magnetized electrons in the limit of fast transit time [1]. A necessary ingredient is a parallel electric field structure, which maintains quasi-neutrality by regulating the electron density, traps a large fraction of thermal electrons, and heats electrons in the parallel direction. Based on the expression for the electron phase space density, equations of state provide a fluid closure that relates the parallel and perpendicular pressures to the density and magnetic field strength [2]. This new fluid model agrees well with fully kinetic simulations of guide-field reconnection, where the parallel electron temperature becomes many times greater than the perpendicular temperature. In addition, the equations of state relate features of the electron diffusion region that develop during anti-parallel reconnection to the upstream electron beta. They impose strong constraints on the electron Hall currents and magnetic fields [3]. For plasmas with low electron beta gradients in the anisotropic pressure can support large parallel electric fields over extended regions. This is important for energization of super-thermal electrons in the Earth magnetotail [4] and perhaps also for fast electrons observed during reconnection events at the sun.

[1] J. Egedal, N. Katz, et al., J. Geophys. Res. 113, A12207 (2008).

[2] A. Le, J. Egedal, et al., Phys. Rev. Lett., 102, 085001 (2009).

[3] A. Le, J. Egedal, et al., Geophys. Res. Lett. 37, L03106 (2010).

[4] J. Egedal, A. Le, et al., Geophys. Res. Lett. 37, L10102 (2010). 

Four variable gamma-ray sources (GeV-TeV) have been associated with binary systems in our Galaxy: the "microquasar" Cygnus X-3 and the "gamma-ray binaries" LS I +61 303, LS 5039 and PSR B1259-63. These objects are all composed of a massive companion star and a compact object of unknown nature, possibly a young pulsar or an accreting black hole. After a brief introduction on gamma-ray astronomy, I will present a comprehensive theoretical model for the high-energy gamma-ray emission and variability in these systems. In this model, the high-energy radiation is produced by inverse Compton scattering of stellar photons on ultra-relativistic electron-positron pairs injected by a young pulsar in gamma-ray binaries and in a relativistic jet in microquasars. I will show that this model explains well the TeV gamma-ray emission observed in LS 5039, but cannot account for the gamma-ray emission in LS I +61 303 and PSR B1259-63. Other processes may dominate in these more complex systems. In Cygnus X-3, the gamma-ray radiation is convincingly reproduced by relativistic Doppler-boosted Compton emission of pairs in a jet. Gamma-ray binaries and microquasars provide a novel environment for the study of pulsar winds and relativistic jets at very small spatial scales.

A necessary condition for magnetic reconnection to occur is the breaking of the "frozen-in" condition for particles flowing in with field lines towards the current sheet separating oppositely-directed magnetic fields. Early simulations of magnetic reconnection relied on resistive MHD to unfreeze ions from field lines by permitting diffusion. Later, the so-called Hall term - usually omitted from MHD - was shown to give rise to separate electron and ion "diffusion" regions. Next, full kinetic (PIC) simulations suggested that kinetic wave turbulence and pressure agyrotropy may affect the reconnection. Most of these simulations were in 2D and assumed antiparallel rather than component reconnection, in which there is an initial out-of-plane magnetic guide field, Bg. We examine the consequences of introducing a realistic initial Bg into 2D and 3D implicit PIC simulations with physical ion-to-electron mass-ratio (1836). Among the new discoveries to be described are the deflection of elongated midplane electron-velocity-jets and the disruption of acompanying highly elongated external "diffusion" regions by very small guide fields commonly found in the magnetosphere. Other electron-scale features of reconnection to be discussed include electron velocity distributions, kinetic instabilities and the spatial structure of electric fields. A number of these features may be detectable by the NASA MMS spacecraft to be launched in 2014.

We have developed a Lorentz force ion, fluid electron kinetic MHD simulation. Different from traditional kinetic or MHD codes, this hybrid model includes full kinetic ions and could be applied to study MHD scale physics. To eliminate the constraint on the timestep due to the fast electron compressional wave, a second-order accuracy implicit method is employed.In this talk, I will present the main equations we are solving, several numerical issues and physics results. For benchmarking, we first studied Alfv'en waves, ion sound waves and whistler waves. Linear results agree well with the analytical theory. Also investigated are the nonlinear evolution of the resistive tearing mode starting from the Harris sheet equilibrium configuration. The linear growth rate and mode structure agree favorably with the resistive MHD theory. In the nonlinear regime, several stages are identified including the secondary island formation, its coalescence with the main island and the nonlinear saturation. In particular, we measured the Rutherford growth rate and the saturation island width for various parameters.

Dr. Alan Kiplinger is a solar physicist at the Center for Integrated Plasma Studies, University of Colorado. He will talk about his recent invited trip to the solar Dutch Open Telescope which is on the island of La Palma off the coast of Northwest Africa. La Palma is a fascinating tropical island with an ancient past, and it has a bright future in astronomy with a myriad of telescopes. These include the surprisingly powerful solar telescope known as the Dutch Open Telescope (DOT) which Dr. Kiplinger was asked to work with in May 2010. The telescope's observations are now dedicated, for 2010, to solar prominences under the coordination efforts of Sara Martin (HelioResearch, La Crescenta, CA) representing the international 'Prominence Research: Observations and Models' team (PROM), and the U. of Utrecht with Dr. Rob Hammerslag. The telescope is itself an amazing mechanical marvel and it is now collecting multiwavelength data of prominence dynamics at unprecedented rates. Dr. Kiplinger will describe experiences on the island, special views of prominences and the DOT.

The Fusion Simulation Program (FSP) Definition Project has been underway for about one year, with the purpose of defining in more detail the Fusion Simulation Program. The purpose of this seminar is to present the status and direction of the planning and to gather community input on the planning and any other related items.

This talk will cover three topics. Collisionless reconnection: inertia of electrons versus their non-scalar thermal pressure tensor as the reconnection mechanism. Energetics of forced magnetic reconnection: forced reconnection as a trigger of magnetic relaxation in an MHD-stable magnetic configuration. On a possible role of secondary tearing instability and plasmoids formation in forced magnetic reconnection.

It is well known that the size of turbulent eddies depends strongly on the velocity shear, making the transport of momentum a key ingredient in any turbulent simulation. However, a self-consistent formulation that includes both the turbulence and the transport of momentum has not been available until recently. One problem is that the turbulent fluctuations have very short wavelengths, on the order of the characteristic size of the microscopic motion of magnetized ions. Thus, a macroscopic fluid description is not valid, and more sophisticated kinetic models are required. The current methodology requires accuracies of 1e-10 to self-consistently evolve the average velocity profiles in a tokamak, whereas the extended formulation to be presented only requires an accuracy of 1e-2.

Magnetic reconnection is a fundamental plasma-physics process involving dramatic rearrangement of magnetic topology and often leading to a violent release of magnetic energy. It is responsible for many disruptive phenomena in laboratory-, space-, and solar physics (e.g., solar flares and magnetospheric substorms). Traditional reconnection research, geared towards these relatively tenuous environments, has so far been limited to electron-ion plasmas with no photons. In contrast, in various astrophysical situations where reconnection is believed to be important, the dissipated energy density is so high that photons cannot be ignored. This, together with some recent laser-plasma laboratory experiments, motivates a new direction of research --- magnetic reconnection in High-Energy-Density (HED) plasmas, where radiation effects (radiative cooling, Compton drag, radiation pressure, and, in more extreme astrophysical cases, pair creation) become important. In this talk, I will first outline the basic general physical ideas behind this new area of research and will then explain in more detail the effect on reconnection of one particular radiative process --- optically-thin radiative cooling.

This talk outlines the goals of the Colorado Field-Reversed Configuration (FRC) Experiment and presents the latest measurements. We use merged spheromaks to study flows and fluctuations in self-organized plasmas. Preliminary measurements using a multi-point (16 positions x 3 axes) magnetic diagnostic indicate that a variety of waves are generated during the merging process. Dispersion relations for coherent waves are extracted from the magnetic data by using a cross-spectral-density correlation technique. Observations during merging include signatures of magnetosonic, L-mode, and ion-cyclotron waves. In order to highlight flow-driven processes, we have designed and constructed a two-point biasing probe for driving bulk E x B flows at subsonic to supersonic speeds. We present first results from the use of the biasing probe.

Magnetic reconnection at Earth's dayside magnetopause creates an "open" magnetosphere, resulting in magnetic flux transfer to the magnetotail. The dynamics of this interaction are dominated by the properties of the solar wind and the interplanetary magnetic field. At Jupiter, the large size of the magnetosphere, rapid rotation, and large internal plasma source ensure that internal processes have a non-negligible effect on the solar wind interaction. The extent of the effect of magnetospheric properties on the solar wind interaction is not well understood; this, along with limited plasma and magnetic field measurements in the outer magnetosphere and magnetosheath has made it difficult to characterize the dynamics at Jupiter's magnetopause. The Cooling study described the motion of reconnected flux tubes on Earth's magnetopause; a proposal to adapt this study to explore the roles of reconnection and viscous interactions at Jupiter's magnetopause will be discussed.

Previous observations have suggested a number of dusty plasma phenomena on the lunar surface, including dust charging, levitation and horizontal transport. These observations include Surveyor images of Horizon Glow (HG), astronaut sketches of dust "streamers" and in-situ measurements made by the Lunar Ejecta and Meteorite (LEAM) experiment. Recent laboratory experiments have approximately reproduced the near surface lunar plasma environment and shown that charging can lead to the levitation and transport of dust grains in a tenuous electron sheath. A critical ingredient to the observed phenomena is the presence of a photoelectron sheath, formed when solar ultraviolet radiation causes the lunar regolith to emit electrons. In order to understand the dynamics of dust particles on the surface of the Moon, the lunar photoelectron sheath has been modeled via a 1-dimensional particle-in-cell (PIC) code. Simulations have focused on the effects of a non-Maxwellian photoelectron velocity distribution and the presence of an incoming solar wind flux. Using the sheath profiles obtained by the PIC code, the charging and dynamics of micron-sized dust grains in the lunar photoelectron sheath are investigated. The presence of non-monotonic sheath potential profiles and their possible impact on the analysis of Lunar Prospector data will also be discussed.

Dust particles detected by sensors on spacecraft carry precious information about their parent bodies. For example, the composition of dust grains ejected from a moon's surface by meteoroid impacts can be analyzed by a dust mass spectrometer on a spacecraft orbiting the moon. Thus, the compositional in-situ analysis of a satellite's surface can be performed even without a lander. High resolution compositional data of dust measured in the vicinity of a dust-producing moon such as Ganymede provides key chemical constraints for understanding the satellite's history and geological evolution.

During recent years the Heidelberg dust group designed and built high resolution mass spectrometers of large and intermediate sensitive areas. An important constraint for the optimum design of the spectrometer's field optics is the properties of the plasma produced by the hypervelocity impacts. Furthermore, the reliable interpretation of a mass spectrum of an impact plasma requires a good knowledge of the various processes that produce the impact plasma. To this aim we performed experiments with a mass spectrometer designed to investigate the energy distributions of the ionized species. Furthermore, we reanalyzed the mass spectra of various materials such as silicates obtained from laboratory experiments using the Heidelberg dust accelerator as well as cosmic water ice dust impacts recorded by the Cassini dust detector CDA. After the initial acceleration the plasma energy was found to be surprisingly low, with a non-Maxwellian distribution. We also investigated which impact parameter actually controls the properties of the impact plasma. Our experiments suggest that this parameter is the energy density at the site of impact rather than the impact speed.

Dr. Konopka is from the Max-Planck-Institut fur Extraterrestrische Physik in Garching and is a candidate for the faculty position associated with the lunar science center. He conducts dusty plasma experiments both in the laboratory and in space. The space experiments are done in the International Space Station in microgravity. Floating dust particles form crystalline arrays that allow exploration of strong coupling and phenomena normally associated with condensed matter. Laboratory experiments with dust in plasma are conducted in high magnetic field (up to 4 T). Two dimensional crystalline arrays rotate rigidly or rotate differentially in concentric shells revealing the relative importance of the Lorentz force and drag forces from ions and neutrals.

Previously flown dust instruments in space were not designed to provide accurate measurement of the velocity of individually detected dust particles. This information, however, can be important to find the source of the cosmic dust and its interaction with the space environment before detection. A future instrument with high trajectory resolution capability could provide a way, for example to a) explore the interaction of interstellar dust particles with the heliosphere, b) enhance the performance of dust sample return missions, c) or enable planetary dust spectroscopy. The Dust Trajectory Sensor (DTS) is an instrument under development to measure the velocity vector of individual dust grains in space. The operation is based on measuring the pickup charge from the dust by an array of wire electrodes. The Coulomb Software is used for the modeling of DTS and simulating the measured signals from particles passing though the instrument. Experimental data (both low and high speed) have been analyzed, which suggests the DTS has a high resolution in speed and angle.

The Framework Application for Core Edge Transport Simulation (FACETS) is a SciDAC proto-Fusion Simulation Program with the aim of performing tokamak core-to-wall transport simulations on massively parallel architectures. The FACETS team has developed a new parallel core transport solver designed to use a variety of transport models, including GLF23, MMM95, NCLASS, and the GYRO gyrokinetic code, and sources, including NUBEAM. The core transport code is coupled to the UEDGE code for two-dimensional transport in the open field region, with the soon-to-be incorporated 1D WALLPSI model for plasma-wall interactions. Parallelism has been an integral part of FACETS since day one, with each component (core, edge, and wall) living on disjoint sets of processors. Coupling between components, which involves the exchange of fields or fluxes at the interfaces, can be implicit. We will report on the status of the FACETS code development, and present initial studies of edge pedestal formation in the DIII-D tokamak.

No Abstract Available 

No Abstract Available 

We have previously developed a Lorentz force ion, fluid electron kinetic magnetohydrodynamic hybrid model. This model has been extended to gyrokinetic electrons. Here we focus on the implementation of an isothermal fluid electron model in the GEM turbulence code. A second-order accurate implicit scheme that generalizes the previous implicit scheme for Lorentz force ions and drift kinetic electrons has been implemented. The generalized Ohm's law is solved for the Harris sheet equilibrium configuration by Fourier decomposing the electric field along the equilibrium field and solving for each Fourier component in the direction perpendicular to the current sheet using direct matrix inversion. Test simulation results include Alfven waves, ion sound waves and the Whistler waves in a slab. And for the Harris sheet equilibrium with a guide field, linear instabilities such as resistive tearing mode is studied.

It is well known that a Hamiltonian system is integrable if it has sufficiently many integrals, and--by Noether's theorem--that each continuous symmetry gives rise to an integral. The resulting dynamics of integrable systems becomes uniform rotation on invariant tori.

What is the analogous structure for volume preserving systems? For the case of incompressible fluids, Bernoulli's theorem can be interpreted to say that an incompressible flow with a symmetry has an integral.This implies that a 3D fluid flow with a symmetry can be effectively reduced to a 2D flow that is Hamiltonian, and therefore integrable. For the case of maps, however, it seems that symmetries and invariants are independent. A 3D volume preserving map with a symmetry can be effectively reduced to an area preserving map. However, this map need not be integrable. To insure integrability requires an additional invariant. The result is similar to a notion of " broad integrability " for general flows defined by Bogoyavlenskij.

Solitary bipolar electric fields have been regularly observed in a wide variety of near-Earth space plasma environments probed by satellites, including the auroral current regions and in the vicinity of magnetic-reconnection sites. Such bipolar fields can indicate the presence of various nonlinear kinetic structures such as electron phase-space holes, ion phase-space holes, and ion solitons -- with electron holes being the most frequently invoked explanation for observed bipolar fields. Among established mechanisms for generating electron holes are the nonlinear saturation of instabilities such as the electron-electron two-stream instability and the electron-ion Buneman instability. Recently, an alternative mechanism involving a "notch" instability has been shown -- through the use of kinetic Vlasov simulations -- to be a potential mechanism for the generation of copious "weak" electron holes. Because the characteristics of electron holes depend on their source mechanism, they have the potential of providing diagnostic information regarding the region where they formed. However, it is first necessary to understand how the properties of holes can evolve as they propagate away from their point of origin to the location where they are observed. To illustrate this idea, a different set of Vlasov simulations will be used to show how electron holes can be accelerated by ambipolar electric fields associated with weak quasineutral density perturbations. 

For the first time, a hot-filament discharge plasma with electron temperature near 200 K has been created continuously in the laboratory. The plasma is created in a double-walled vacuum chamber with the inner wall cooled by liquid nitrogen to 110 K. With 1.6 mTorr carbon monoxide at 140 K, the electron temperature is 19 meV (217 K) and the density is 4.7 x 108 cm-3. Electron temperatures are much higher with cooled Ar, He, H2, and N2. Electron cooling is greatest in CO because the heteronuclear CO molecule has a nonzero electric dipole moment which increases the cross section for electron energy exchange. The resulting plasma is unique in that electron-ion collisions are more frequent than electron-neutral collisions (even though the plasma is partially ionized) and recombination of ions and electrons is primarily into Rydberg levels. This plasma is also nearer to the strong coupling limit (lower Coulomb logarithm) than other continuous plasmas.

Detailed knowledge of the lunar plasma environment is of critical importance to the design of human habitats and instruments for future lunar missions. While theories for the lunar plasma environment have been developed for decades, large scale numerical simulations of the lunar plasma have only recently become feasible. These simulations can help to answer fundamental questions about the charge density distribution on the lunar surface as a function of local time, the plasma density distribution above the surface and its change with time, merging of the photo-electron layer with the solar wind and the distribution of local electric fields. The goal of this project, which is part of the Colorado Center for Lunar Dust and Atmospheric Studies, is to model the lunar plasma environment from first principles using the widely used plasma simulation code VORPAL. In this presentation we will summarize ongoing kinetic simulations of the lunar plasma environment. After initial comparisons of 1D simulations with theory, we will investigate the effect of topologies on the sheath properties in 2D and 3D.

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Electron holes have been associated with the current sheet of magnetic reconnection by space observations and experiments. The development of these electron holes is poorly known. Using particle-in-cell simulations and kinetic theory, we investigate the formation of electron holes. We found that Buneman instability occur first and form slow-moving electron holes. After the saturation of Buneman instability, Buneman, electron-electron two stream and lower hybrid instabilities compete with each other. Both electron two-stream and lower hybrid instabilities can dominate. The increasing phase speeds of these two instabilities can transfer the momentum from high velocity electrons to low velocity electrons and form accelerating- fast-moving electron holes. In particular, if Buneman and lower hybrid instability dominate, both slow-moving and fast-moving electron holes can co-exist at the same location. The coherent relation between phase speed keep these electron holes stable. The phase speed of lower hybrid instability play an important role in determining which instability will win: Buneman or two-stream instability.

In August of 2007 two sounding rockets were launched from the Andoya Rocket Range, Norway carrying the MASS instrument (Mesospheric Aerosol Sampling Spectrometer). The instrument detects charged aerosols in four different mass ranges on four pairs of biased collector plates, one set for positive particles and one set for negative particles. The first sounding rocket was launched into a Polar Mesospheric Summer echo (PMSE) and into a Noctilucent Cloud (NLC) on 3 August. The solar zenith angle was 93 degrees and NLC were seen in the previous hour at 83 km by the ALOMAR RMR lidar. NLC were also detected at the same altitude by rocket-borne photometer measurements. The data from the MASS instrument shows a negatively charged population with radii >3 nm in the 83-89 km altitude range, which is collocated with PMSE detected by the ALWIN radar. Smaller particles, 1-2 nm in radius with both positive and negative polarity were detected between 86-88 km. Positively charged particles <1 nm in radius were detected at the same altitude.

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The well-known guiding center (GC) model for charged particle motion in a strong magnetic field separates the particle's motion into a fast gyration around a magnetic field line, superimposed on the gyration-averaged motion of its guiding center. Expanded in small gyroradius, the first order equations of motion can be derived directly from the particle motion. At higher order, the equations have only been derived using a noncanonical Hamiltonian or Lagrangian formulation. The result is valid to all orders in a uniform straight magnetic field. In three dimensions, however, the twisting of the magnetic field due to torsion imposes a separate geometrical existence condition that is completely independent of the Lagrangian formalism. In 3D magnetically confined plasmas, this condition is not usually satisfied, since finite torsion is directly related to the presence of parallel plasma current. It can be satisfied in exactly 2D configurations, such as toroidal axisymmetry. The breakdown of the GC expansion appears to be related to the appearance of chaos in Hamiltonian systems.

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Magnetic islands are frequently observed in high-performance tokamak plasmas. These islands limit the achieved plasma performance and are of concern for next-generation burning plasma experiments. Modern gyrotron sources have been used to stabilize these islands using Electron Cyclotron Current Drive (ECCD). The ITER device is currently planning on using this technique to stabilize the magnetic islands; however, uncertainties exist regarding the amount of power needed for island stabilization. Computational modeling of ECCD-stabilization of islands would allow better extrapolation of current experiments to ITER, but quantitative prediction requires accurate modeling of the current drive and of island dynamics. The Simulation of Wave Interactions with MHD (SWIM) SciDAC project is a collaboration of different groups to enable this modeling. In this talk, we present the development of the mathematical formalism for simulating RF-stabilized tearing modes, and initial simulations of feedback stabilization.

The Colorado FRC is a local experiment designed to study turbulence, flow, and stability in a field-reversed configuration (FRC). The FRC is a self-organized, high-beta plasma that provides a unique laboratory for basic plasma physics as well as fusion energy research. In this introduction to our ongoing research here in CIPS, I will provide a brief overview of the physics of compact toroids, describe the Colorado FRC machine and diagnostics, discuss current and planned experiments, and present recent results.

I'll talk about some recent progress in the simulations and observational studies of magnetic reconnection. With full kinetic particle-in-cell simulations, the work is to address two issues: how does fast reconnection initially grow, and what decides the evolution of the reconnection rate. The fast reconnection onset is discovered to be a nonlinear electron self-reinforcing process. Accelerated by the reconnection electric field, the small portion of energetic electrons in the vicinity of the X point could enhance the reconnection rate. During the later stage, the reconnection rate was thought to be throttled by the elongation of the electron diffusion region (EDR). Yet a new satellite observation found that the EDR could be very long and the reconnection rate remains fast. Here we find the change of reconnection rate is not controlled by the length of the EDR, but rather by the availability of plasma inflows from upstream. These results may give us some new insights to the macro-micro coupling process of reconnection.

I will discuss radiofrequency (RF) ion traps used at the National Institute of Standards and Technology (NIST) in quantum information experiments. In these traps linear crystals (or strings) of beryllium ion qubits (two-level quantum systems) are confined in segmented multi-zone electrode structures. The harmonic motion of the trapped ions is laser cooled to the quantum mechanical ground state. Strong Coulomb coupling between ions provides the basis for quantum gates mediated by phonon exchange. Quantum information processing with many qubits requires trapping and transport of many ions in structures with many trapping zones. I will describe current efforts at NIST toward achieving this goal through the construction of microfabricated RF ion trap arrays.

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We have compiled a cross section set for H+, H2+, H3+, H and H2 collisions with H2 that is consistent with collision theory and experiment and with our measured absolute Halpha emission, Halpha Doppler profiles, near-UV molecular H2 continuum emission, ion energy distributions at the cathode, transient currents, and transient Halpha emission. Our measurements used a very low current, uniform electric field drift tube so that hydrogen dissociation and plasma electric fields are negligible. At the higher electric field to gas density ratios (E/N = 10 kTd and mean H+ ion energies of ~ 300 eV), the principle source of Halpha and continuum excitation is collisions of H with H2. At our lowest E/N of 350 Td (mean H+ energy ~ 40 eV) electron excitation dominates, but excitation by H atoms is still observed. Brief references will be made to the initial application of these results to glow discharges, inertial electrostatic confinement devices, edge plasmas of fusion devices, auroral Halpha emission from the outer planets, and evaluation of experimental evidence for hydrinos.

The talk will be an overview of the interdisciplinary field of dust research starting with fundamentals of dusty plasma through the interaction of cosmic dust with the upper atmosphere, the dusty surface of the Moon and ending with the recent discovery of interstellar dust within the solar system. Dust particles immersed in plasmas will acquire charge and introduce a variety of new phenomena, including dust acoustic waves and the formation of crystal-like structures. The upper atmosphere is the place where incoming meteoritic dust particles ablate and re-condense back to nanometer size smoke particles. These particles provide the seed for the nucleation of water ice in the summertime polar mesosphere that is exhibited as visible noctilucent clouds or as a layer with large radar backscatter. On the Moon, there are several in-situ and remote sensing observations that indicate that dusty plasma processes are likely to be responsible for the mobilization and transport of lunar soil. These observations remain largely unresolved today. In 1992 the dust detector on the Ulysses spacecraft identified interstellar dust passing through the solar system. A new and exciting opportunity is now open to directly sample these fundamental building blocks of the Universe.

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In an effort to increase the luminosity of Brookhaven National Lab's Relativistic Heavy Ion Collider (RHIC), a novel electron cooling system has been proposed. Although the ions and electrons are highly relativistic in the lab frame, their motion is non-relativistic in the beam frame. The dynamics share similarities with the classical n-body problem of astrophysics. In arbitrary external fields, the dynamical friction force on ions (and, hence, the cooling rate) is difficult to estimate. We present numerical algorithms that simulate the friction force from first principles. This is a challenging regime for electron cooling due to the high energy of the ions, and the design of the cooling section has changed several times over the past few years. We will discuss design trade-offs and numerical simulations of each design.

The spontaneous formation of electric current sheets in a magnetic-field dominated, electrically highly conducting plasma is a physically attractive process to explain the heating of the solar corona. Current sheets can reach such thinness via nonlinear ideal MHD as to dissipate with the resistive reconnection of magnetic fields despite a high but finite conductivity. Thus highly conducting plasmas are necessarily also resistively heated under astrophysical circumstances. X-ray astronomy has revealed that most solar-type stars have million-degree hot coronae. The hot corona is therefore a universal astrophysical phenomenon. The theory of this process due to E. N. Parker will be illustrated with a recent direct theoretical demonstration of current-sheet formation. The mathematics of the demonstration is remarkably simple but its physical implications seem far reaching.

The MASS (Mesospheric Aerosol Sampling Spectrometer) rocket campaign was conducted from the Andoya Rocket Range the first week of August 2007 coincident with the German-Norwegian ECOMA rocket campaign. The two MASS rockets carried electrostatic mass analyzers for the charged fraction of the aerosol particles in noctilucent clouds (NLC). The mass analyzer was mounted on the tip of the payload and pointed in the ram direction. Aerosol particles with different ranges of charge-to-mass ratio were collected within the instrument housing on two sets of four biased collector plates, with one set for positive particles and one set for negative particles. The first rocket was launched into NLC on 3 August approximately 26 minutes after an AIM (Aeronomy of Ice in the Mesosphere) satellite overpass. NLC were seen earlier in the day at 83 km by the ALOMAR RMR lidar pointed along the rocket trajectory. The data show the density of negative particles with radius greater than 3 nm rising sharply at 83 km and continuing to 89 km, collocated with PMSE (Polar Mesosphere Summer Echo) detected by the ALWIN radar. Particles with 1-2 nm radii with both signs of charge and positive particles with less than 1 nm radius were detected at 86-88 km. Initial charge-density estimates are several thousands per cubic centimeter for each of these size ranges.

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Turbulent transport driven by Collisionless Trapped Electron Modes (CTEM) is systematically investigated using three-dimensional gyrokinetic delta-f Particle-In-Cell (PIC) simulations. Scalings with local plasma parameters, including density gradient R/Ln, electron temperature gradient R/LTe, magnetic shear S hat, electron to ion temperature ratio Te/Ti and the inverse aspect ratio r/R, are studied. Simulation results are compared with previous simulations and theoretical predictions. Zonal flow suppression in nonlinear CTEM turbulence depends on electron temperature gradient and electron to ion temperature ratio. We introduce zonal density as another nonlinear saturation mechanism in the parameter regime where zonal flows are unimportant. The generation of zonal density is explained by a mode coupling model that agrees with the simulation. The mode coupling model also shows how the zonal density can stabilize the most unstable mode, which qualitatively agree with the simulation results.

In gyrokinetic simulation of turbulent transport in tokamak plasmas using the delta-f particle-in-cell (PIC) method, it is frequently observed that the mean-square-value of the particle weights continue to grow after the turbulent fluxes reach a steady state. This is "the Growing Weight Problem" in PIC simulations. Since the particle weights are defined to be proportional to the distribution function, a situation where the particle distribution function continues to grow but the turbulent fluxes reach steady state is paradoxical. I will show how this "energy paradox" is resolved by examining the entropy evolution of the plasma. A numerical scheme for solving the growing weight problem will be described. Delta-f is periodically deposited on a five-dimensional phase-space grid, then re-evaluated at the particle position using interpolation. Using three-dimensional toroidal Ion-Temperature-Gradient Driven turbulence as an example, the numerical scheme is demonstrated to effectively suppress the long-term increase of the particle weights, while keeping the turbulent flux unchanged.

Xenon ion laser-induced fluorescence (LIF) measurements in low temperature Xe I I plasmas (Te ? 1eV , Ti ? 1/40eV , ni ? 10 9 cm?3 ) have been achieved. The transition studied involves the metastable state (3 P1 )5d [3]7/2 , at 108423.07 cm?1 . The LIF scheme involves transitions which have been misidentified in the literature. At any rate, these studies have permitted measurements of the ion velocity distribution functions for both ions in a two ion species (Ar+Xe) plasma, so as to make possible the first experimental tests of the Generalized Bohm Criterion. Is the Bohm Criterion satisfied in multiple ion species plasmas? Come to the seminar and find out!

Observational evidence for localized electrostatic field structures in a variety of near earth space plasma environments is now well established. The most frequent such observations are of the typically bipolar parallel electric field signatures of electron and ion phase space holes. However, another class of nonlinear structures double layers with their less frequently observed unipolar parallel fields, may in fact play a more important role in regions such as Earth's auroral ionosphere. In particular, a double layer is able to support a large parallel potential drop over a short distance, thereby contributing directly as well as indirectly to the acceleration of both electrons and ions. Kinetic plasma simulations are important tools for the purpose of studying the dynamics of double layers and phase-space holes. Simulations based on direct integration of the Vlasov equations, while less commonly employed than particle simulations, have proven to be particularly well-suited to this effort. Because standard Vlasov methods become numerically demanding when modeling systems in more than one spatial dimension, various "reduced" Vlasov algorithms have been developed to facilitate these studies. Results of recent Vlasov-based simulations will be presented, addressing issues such as the stability and perpendicular structure of double layers, as well as their role in the generation of phase-space holes and the perpendicular heating of ions.

The application of electric fields to flames has been studied at least as far back as 1814, was applied to flame combustion in the 1920's and was further developed into several applications in the last half of the 20th Century. When the electric field strength is sufficient to cause electrical breakdown of a fuel or fuel/air mixture, plasma effects will dominate. Plasma effects can increase electron and ion temperatures and promote combustion through the formation of 'active' species (such as free radicals) or the dissociation of fuel molecules into smaller, more-easily combusted fragments. Plasma-assisted combustion (PAC) is now a timely topic worldwide, possibly having applications that can allow more efficient fossil-fuel usage, the conversion of low-grade fuels into higher-grade fuels, and the reduction of pollution through ultra-lean burn combustion. This chapter focuses on non-equilibrium ("cold" or "non-thermal") plasma applications to combustion, particularly for enhancing combustion stability, efficiency, and reducing undesirable emissions. This is in contrast to equilibrium ("hot" or "thermal") plasmas (e.g., spark plugs, plasma jets/torches). This talk will present a brief historical background on electric field and plasma effects on combustion and will then discuss non-equilibrium plasmas, as mainly applied to combustion stability, efficiency, and pollution reduction in more detail. Plasma-based ignition will be only briefly mentioned because it is considered a specialized, although important, topic within the PAC field. Selected examples from the literature will be presented, but the talk will primarily focus on work carried out at the author's institution that provides examples of nonequilibrium plasma applications to combustion enhancement. In non-equilibrium (or non-thermal) plasmas, energetic electrons are primarily responsible for generating the desired chemical species relevant to combustion, while the ions and background gas are 'cool'.

While the PEP II luminosity recently reached a new peak of 10^34 cm^?2s^?1, simulations show that this peak can be doubled in the future by changing certain parameters. Luminosity is generally defined as a phase space overlap integral of two colliding beams and is a measure of the performance of the collider. The PEP II B-factory is an electron-positron collider located at SLAC. This talk will begin with a few details of the PEP II facility, an introduction to the physics of beam-beam interaction, followed by a brief explanation of the simulation method. Finally, results will be presented that led to determining the final set of parameters that yielded a simulated luminosity of 2x10^34 cm^?2 s^?1. Besides this, results will also be presented showing that the current peak luminosity can be immediately increased by about 10% by choosing an optimum set of accelerator parameters.

Planetary surfaces exposed to the solar wind and high energy solar radiation develop a charge due to photoemission, collection of solar wind electrons and ions, and secondary electron emission. Dust particles on the surface can be lifted off the surface and transported by the plasma sheath electric field. Observations of a lunar "horizon glow" by several Surveyor spacecraft on the lunar surface in the 1960s and detections of dust particle impacts by the Apollo 17 Lunar Ejecta and Meteoroid Experiment (LEAM) have been explained as the result of micron-sized charged particles lifting off the surface. The NEAR/Shoemaker spacecraft observed unusual deposits of fine material in some craters on the asteroid Eros that may be the result of electrostatic transport of dust. I will give an overview of observations from the Moon and Eros and numerical simulations of the process of charged dust transport in a dayside photoelectron sheath.

The interaction of the solar wind with the Earth's magnetic field creates several large sheets of electric current, including the ~10 MA tail current sheet which flows above geosynchronous orbit. A variety of nonlinear plasma processes occur within this sheet and its dynamics control much of the Earth's magnetosphere. Understanding its equilibrium configuration is thus an important step in resolving broader issues including current-driven instabilities, reconnection and the overall dynamics of the magnetosphere. Despite the large physical size, the equilibrium structure is frequently too thin to be describable within the framework of magnetohydrodynamics; consequently, realistic models must be built with Vlasov-Maxwell theory. Detailed observations of the tail current sheet are available from many satellites, most notably a set of 4 European Space Agency satellites known as Cluster. However, by comparing Cluster observations to available current sheet models, it becomes clear that the existing models are generally insufficient for describing the configuration. By using the observations as a guide, I will discuss the generalization of an existing class of models to create an exact semi-analytic Vlasov model that can better represent the real tail current sheet.

This seminar will focus on the operating principles and capabilities of ion thrusters. Processes applied to generate energetic electrons and thence ions, to extract and accelerate the ions, and to neutralize the resulting ion beam will be discussed. The reasons why these thrusters are being used so successfully for stationkeeping and orbit-raising missions on Earth satellites and why they were so successful on the Deep Space One mission will be mentioned. Numerical modeling results that describe the ion extraction and acceleration process will be compared to corresponding experimental results obtained using small arrays of ion extraction aperture pairs (gridlet studies). The great potential of electric thrusters for future advanced satellite and exploration missions including NASA's DAWN mission will be mentioned.

Beam-target fusion is not of economic interest, as the beam drag power exceeds the fusion yield. This picture changes if one imagines using the heat produced by beam drag as a low entropy source (because of the high plasma temperature) rather than exhausting it. This elementary thermodynamics is fine, but the challenge is in the (conceptual) engineering. How to arrange a confined plasma to form a high efficiency heat engine and how to use the mechanical energy to form a beam? Known electrostatic fusion concepts are extended to "conventional" magnetically confined quasi-neutral plasmas. Rapidly (supersonic) rotating plasmas are particularly useful for this. The rotation forms a mechanical energy reservoir and the cross field electrical potentials are useful for particle acceleration.

In this talk, two new physics ideas are developed and applied to this problem. First idea: electrostatic wells are replaced by centrifugal wells and non-neutral plasma replaced by quasi-neutral plasma. Previously known physics are applied, leading to many arrangements which form a high-efficiency (<90%) heat engine. Simplest of all is the Pastukov problem, in which a single well confines a low-collisionality nearly thermal plasma. It is shown that a proper arrangement of magnetic field (essentially the open field of a field-reversed configuration - FRC) can make this into a heat engine, so that plasma heat becomes rotation. The energy cycle is completed by converting rotation to beam energy. It is shown how to use the high electrical potentials induced by rotation to electrostatically accelerate a beam into the confined plasma.

Second idea: plasma rotation can produce plasma waves from a static magnetic perturbation, using nothing more than the Doppler effect. These waves can also be used to produce a desired beam by resonant absorption. Another use for such waves is to drive currents. As already demonstrated experimentally, such currents can form a FRC.

All of this leads to lowering the fusion threshold. In particular, required temperatures are greatly reduced, leading to very small, very high-power density systems. The non-thermal fusion also means that aneutronic fuel cycles can be used. Some examples are given. Finally, a small experiment to test these physics is being planned and some details of this design are given.

Metamaterials are artificial periodic structures made of small elements and designed to obtain specific electromagnetic properties. As long as the periodicity and the size of the elements are much smaller than the wavelength of interest, an artificial structure can be described by a permittivity and permeability, just like natural materials. When the permittivity and permeability are simultaneously negative in some frequency range, the metamaterial is called double negative or left-handed and has some unusual properties. Left-handed metamaterials (LHM) have potential applications in active and passive devices at millimeter waves and at much higher frequencies. Waveguides loaded with metamaterials are of interest because the metamaterials can change the dispersion relation of the waveguide significantly. Slow backward waves can be produced in a LHM-loaded waveguide without corrugations. The dispersion relation of a LHM-loaded waveguide has several interesting frequency bands which are described. Left-handed structures can be employed at X-band accelerators to suppress wakefields.

Plasma sputtering can greatly reduce the size of charged dust grains orbiting within the magnetosphere of Saturn in only a few decades.With mass and charge varying in time, the resulting equations of motion are non-hamiltonian. Except for the small influence of solar radiation pressure, this system is axisymmetric and the question arises as to the existence of global invariants in the absence of a hamiltonian. For larger grains, where gravity dominates we show that a formal hamiltonian may be constructed by treating the velocities as canonical momenta. For smaller grains, where the planetary magnetic field dominates, a hamiltonian description is apparently not possible. Nevertheless, an exact invariant is derivable from the axisymmetric equations of motion. Implications for the history and structure of Saturn's E ring and for observations by the Cassini orbiter CDA and UVIS experiments will be discussed.

Current mechanisms of coronal mass ejection (CME) initiation tend to rely on ad hoc assumptions to energize coronal magnetic fields to erupt. Most notably, artificial shearing of coronal magnetic arcades has been employed for nearly three decades to model flares and CMEs while no self-consistent explanation for the shearing motions was known. This talk will focus on the recent discovery that such shearing motions are driven by the Lorentz force that naturally arises when bipolar magnetic fields emerge from the photosphere into the corona. These spontaneous shearing motions will be shown to produce eruptions in a fully self-consistent manner in both magnetic arcades and flux ropes. The shearing motions transport axial flux and energy from the submerged portion of the field to the expanding portion, strongly coupling the solar interior to the corona. This physical process is very robust for explaining the highly sheared state of the magnetic field associated with prominences, and why these magnetic fields erupt in flares and CMEs.

Spontaneously arising magnetic fields occur widely throughout the universe. Attempts to explain them go back at least to Gauss in 1838 and define the "magnetic dynamo problem." In the context of magnetohydrodynamics (MHD), it is easy to see that some of the possible motions of an electrically-conducting fluid are capable of amplifying arbitrarily small magnetic fields. If the amplification continues, the magnetic fields B and their associated electric currents J become large enough that the Lorentz force JxB ceases to be negligible and begins to participate nonlinearly in the mechanical motion of the fluid, which sometimes may be turbulent. The difficulty lies in making the results quantitative and in accountng for the kinds of magnetic fields (planetary, solar, laboratory, or remotely astrophysical) that are created and observed. We have been doing numerical MHD computations motivated jointly by recent laboratory experiments on liquid sodium (e.g., [1,2]) and the need to account for magnetic fields generated inside spheres [3] in planetary models. An important number is the ratio of fluid viscosity to resistivity (in dimensionless units, the "magnetic Prantdl number"); it has much to say about the ease or difficulty of exciting dynamo processes. The subject will be reviewed at an elementary level, and then samples of our recent computations discussed.

[1] A. Gailitis et al, Phys. Rev. Lett. 86, 003024 (2001).

[2] P.D. Mininni and D.C. Montgomery, Phys. Rev. E72, 056320 (2005).

[3] P.D. Mininni and D.C. Montgomery, "Magnetohydrodynamic activity inside a sphere," arXiv:physics/0602147 (submitted to Phys. Fluids, 2006).

We investigate the effect of mass loss on the invariants of systems having translational or rotational symmetry. These systems are nonhamiltonian in the physical momenta but, in the case of non-velocity-dependent potentials can be made formally hamiltonian by treating the velocities as canonical momenta. Applying Noether's theorem to the formal Hamiltonian then yields global invariants corresponding to its symmetries. For velocity-dependent potentials such as occur for motion in magnetic fields, an exact invariant is constructed from the (nonhamiltonian) vector field. For adiabatic orbits the motion is thereby reduced from 3D to a 2D manifold with time-dependent effective potential parametrized by the conserved momentum. The results are applied to single particle motion in an axisymmetric gravitational field, the time-dependent Kepler problem, and charged particle motion in linear and axisymmetric magnetic fields. Finally, we indicate how the results might be combined to describe the motion of charged dust grains about Saturn.

Observations from auroral satellite missions have shown for decades that electron and ion distributions in the auroral region are consistent with being accelerated through magnetic field aligned electric fields (so called parallel electric fields). More recently, FAST (an auroral spacecraft), has directly measured parallel electric fields. However, in a collisionless plasma, there is no generally accepted theoretical description of how parallel electric fields are self-consistently supported.

In this talk, I will show that parallel electric fields can be supported by double layers (DL). I will then show how we solve for such a double layer using methods similar to Bernstein, Green and Kruskal [1957] (the so called BGK method). The distribution functions that we use to construct the DL are modeled from FAST data. Finally, to test whether such a DL is stable, I have initialized a Vlasov simulation with a typical auroral cavity plasma, and have included a double layer to see how it evolves. I will briefly discuss the Vlasov algorithm for evolving distribution functions. One of the new features of the simulation is that we have included two ion species (H+ and O+) in addition to electrons. As a result of having two ion species, I will show how ion phase space holes and other non-linear structures, which are often seen with FAST, form in the simulation.

The delta-f algorithm has been implemented in the particle-in-cell (PIC) code VORPAL. With this approach, the mode conversion from the extraordinary (X) mode to the electron Bernstein wave (EBW) below and above the second electron cyclotron harmonic frequency is simulated. It is found that a full X-B mode conversion below the second cyclotron harmonic frequency can be established for the parameters optimizing the maximum mode conversion efficiency coefficient giving by the linear theory. When the driving frequency is in the vicinity of the third and fourth cyclotron harmonics, however, the mode conversion becomes less efficient even for the optimized parameters. A new X-B mode conversion scenario due to the complicated dispersive behavior of the EBW is revealed in which the present linear theory of X-B mode conversion may fail. It is also shown that the mode conversion and propagation of EBWs are affected by the existence of the electron cyclotron harmonic resonance. If the amplitude of the incident X wave is sufficiently large, resonant mode-mode coupling is observed in the X-B mode conversion.

Collaborators: John R. Cary, Daniel C. Barnes and Johan Carlsson

The goal of inertial confinement fusion research is to create miniature thermonuclear energy bursts. This requires heating and compressing a deuterium-tritium mixture to stellar interior conditions in a terrestrial laboratory. The dynamic hohlraum approach converts electrical energy from the Z pulsed power machine into x-rays that drive spherical capsule implosions. The hot dense implosion core plasma emits thermonuclear neutrons and x-rays that are used to diagnose and optimize the implosion. In particular, Ar tracer atom emission is measured with time- and space-resolved spectrometers that provide data suitable for a tomographic reconstruction of the implosion core temperature and density profiles. The challenges and opportunities provided by dynamic hohlraum fusion research will be described.

We have detected thermally excited charge fluctuations in a pure electron plasma over a temperature range of 0.05 < kT < 10eV. These fluctuation spectra have both a global mode component and a random particle fluctuation component.

At low temperatures, the m? = 0, kz = 1, 2, 3, . . . Trivelpiece-Gould modes (standing waves of density fluctuation along the z-axis; i.e., center of mass motion, breathing mode, and higher modes) are weakly damped and dominate, since the random particle component is suppressed by Debye-shielding. As the temperature increases, the broad random particle component increases in between the modes. The thermally excited mode is physically interesting because it exhibits both the individual particle behavior and the collective mode (wave) behavior of equilibrium plasmas. Also, the thermally excited mode leads to an important application, which is a passive temperature diagnostic of electron plasmas.

Flows and magnetic fields are primary actors in many processes in space and solar environments. Understanding the interplay of flows and magnetic fields is key for developing a predictive model of processes involving energy conversion between magnetic and kinetic energy. Processes where these issues are paramount include coronal mass ejections, solar wind formation and magnetic disturbances in the space weather around the Earth.

In the present seminar, I describe my recent work in the field of flow-magnetic field interaction applied to processes typical of the solar and Earth environment. I will describe the specific examples of the genesis of the slow solar wind in the solar corona and of reconnection in the Earth's magnetosphere. I will describe fundamental processes related to the interplay of flows and magnetic fields and I will address how microscopic and macroscopic processes interact to determine the overall evolution. A unique tool to handle such multiple scale problems at within a fully kinetic approach, CELESTE3D, will also be described.

For the last several years Advanced Energy has worked in the development of plasma and ion sources. These development efforts encompass activities ranging from basic research to product and application development. During the first part of this talk we will present, as an example of basic research, the study of transient phenomena in planar magnetron discharges. It will be shown that high-speed imaging reveals interesting details of the dynamics of arcs occurring on these discharges, and can be used to estimate the drift speed of electrons on cross-field configurations. The second part of the talk will describe some of our products and the commercial applications they are used in.

Charged dust grains orbiting Saturn are subject to the simultaneous influence of several different forces, including planetary gravitational and electromagnetic forces, plasma drag, and solar radiation pressure. In addition, sputtering produced by the erosive magnetospheric plasma leads to a significant diminution of submicron grain radii in a matter of decades. As it shrinks, a grain becomes more responsive to the electromagnetic forces, while the topology of the confining effective potential undergoes qualitative changes. At the same time the motion becomes more chaotic and therefore increasingly ergodic. The synergism of topology and ergodicity can lead to significant particle loss to the planet or to interplanetary space, while more regular orbits can remain trapped by local invariants. In addition, the symmetry-breaking effects of radiation pressure can enhance chaos, while planetary oblateness J2 can contribute to orbital ergodicity. The results are applied to the CDA experiment on the Cassini Spacecraft now orbiting Saturn.

The well developed linear theory of ion-cyclotron range of frequencies (ICRF) wave interactions with plasma has enjoyed considerable success in describing antenna coupling and wave propagation, and provides a well-known framework for calculating power absorption, current drive, etc. in fusion experiments. In some situations, less well studied nonlinear effects are of interest, such as rf driven flows, ponderomotive forces, rf sheaths, and related interactions with the edge plasma. A tutorial-style overview of these effects will be presented, concentrating on basic rf-plasma-interaction physics. For fast waves, the parallel electric field near launching structures is known to drive rf-sheaths which can give rise to convective cells, interaction with plasma "blobs", impurity production, and edge power dissipation. In addition to sheaths, ion Bernstein waves in the edge plasma are subject to strong ponderomotive effects and parametric decay. In the core plasma, slow waves can sometimes induce nonlinear effects. Mechanisms by which these waves can influence the radial electric field and its shear are summarized, and related to the general (reactive-ponderomotive and dissipative) force on a plasma from rf waves. It is argued that there are significant opportunities now for new predictive capabilities by advances in integrated simulation of these mechanisms.

*In collaboration with D.A. D'Ippolito, D.A. Russell [Lodestar], L.A. Berry, E.F. Jaeger, and M.D. Carter [ORNL]

** Work supported by U.S. DOE grant DE-FG02-97ER54392 and the RF-SciDAC project.

It is quite possible that nuclear fusion will be the only source that can provide the prodigious power demands that the world will face in the future. The difficulty however for most nuclear fusion concepts is the complexity and large mass associated with the confinement systems. The challenge that the fusion community is faced with today is a consequence of this scaling. The high cost of tokamak research (and thus reactors) is primarily due to the large reactor sizes required for fusion gain with low steady state plasmas (being the ratio of the plasma to magnetic energy density). At the other end of the spectrum, for most pulsed devices, the mass and complexity of the fast energy delivery systems (lasers, liners, beams etc.) become the problem. It is the contention here that a simpler path to fusion, that avoids many of these major difficulties, can be achieved by creating fusion conditions in a different regime at small scale (rp ~ a few cm). A new experimental program has begun that will take advantage of developments in the very compact, high energy density regime of fusion employing a plasmoid commonly referred to as a Field Reversed Configuration (FRC). The FRC is a closed field configuration where the confining magnetic field is provided by plasma toroidal currents alone. Of all fusion reactor embodiments, only the FRC has the linear geometry, low confining field, and intrinsic high plasma required for magnetic fusion at high energy density. Most importantly, the FRC has already demonstrated the confinement scaling with size and density required for fusion at high density. A fusion reactor based on the formation, acceleration, and compression of the FRC will be presented.

Phase contrast imaging diagnostic (PCI) is an internal reference beam interferometric technique which has been used successfully in high temperature tokamak plasma experiments to image the line integrated plasma density fluctuations. The diagnostic exploits the insertion into the beam path of a 1/8 deep grooved "phase plate" which then allows measurement of wavelengths and correlation lengths of fluctuations propagating perpendicular to the laser beam (near forward scatter). In the Alcator C-Mod and DIII-D tokamak PCI experiments a CO2 laser beam is used to probe both low frequency (f?1 MHz) instabilities and high power launched RF waves (80 MHz) in the ion cyclotron range of frequencies. The modes studied in the past in Alcator C-Mod include the so-called "quasi-coherent mode" (an edge ballooning fluctuation localized to the edge pedestal), semi-coherent TAE -like modes, including Alfven wave cascades, low frequency turbulence, and high power launched ICRF waves. The ICRF waves are detected by a heterodyne technique assist using optical modulation of the laser beam. The ICRF wave propagation studies have revealed an important aspect of mode conversion phenomena in multi-ion species plasmas, namely that in the typical case of sheared magnetic fields in tokamaks, mode conversion into kinetic ion cyclotron waves (the shear wave branch) may dominate over that into electrostatic ion Bernstein waves. This has important implication for using these waves to drive currents or generate shear flow in tokamak plasmas. In DIII-D, PCI diagnostic has been used to study low frequency turbulence during L to H mode transition, ELMS, and coherent edge modes during the Quiescent H-mode. Signatures of zonal flows have also been observed in past experiments. While most of the past studies were limited to wavelengths equal or longer than the ion gyro-radius (kri ? 1, f ? 1MHz ), new upgrades to the electronics will allow detection of wavelengths and frequencies in the electron gyro-radius regimes (kre ? 1, f ? 10MHz). This new capability will allow us to study the electron temperature gradient modes and the trapped electron mode, both being candidates for determining electron transport in magnetically confined plasmas. While spatial localization of long wavelength modes along the PCI laser beam is often lacking, in the short wavelength regimes in a sheared magnetic field localization can be achieved by using a rotating masking plate in conjunction with the phase plate. I will describe some of the results and the upgrades being implemented now on both C-Mod and DIII-D.

Acknowledgements:

This work is being supported by the US DOE, OFES Novel Diagnostics Initiative.

Key contributions to the PCI diagnostic by J. Dorris and C. Rost (at DIII-D), N. Basse, L. Lin, and E. Edlund (at C-Mod) are acknowledged. In addition, key contributions to the C-Mod ICRF physics by P. Bonoli, Y. Lin, J. Wright, and S. Wukitch are noted. Past contributions by S. Coda, A. Mazurenko and E. Nelson-Melby are also noted here.

Plasmelt Glass Technologies LLC (Plasmelt) is developing and testing a full-scale, modular, high intensity, plasma melter capable of producing 500-1500 lb/h (230-680 kg/h) of high-quality glass. The melter uses a remotely-coupled arc that operates at power levels up to 1.4 mW at atmospheric pressures. This presentation will discuss the theory behind the remotely coupled plasmas and the current and future industrial applications of this technology.

The Field Reversed Configuration (FRC) is a compact toroidal equilibrium that appears to relax to a state with large pressure gradients. Related fundamental plasma physics questions extend beyond MHD models, and are relevant to geophysical and astrophysical phenomena. The very successful Taylor paradigm for relaxation to a zero pressure, force free state does not apply. The FRC has large b, and can confine large plasma pressure for a given magnetic field. FRC's are interesting because they have vanishing rotational transform, magnetic shear, and helicity. The equilibrium is thought to be dominated by cross-field diamagnetic current and strong flows. Stability lifetimes greatly exceed Alfvén times and defy MHD predictions. Magnetic reconnection and anomalously large resistivity drives essential ohmic dissipative heating. At Los Alamos National Laboratory, we have formed high density, high b FRC's for use as a target for Magnetized Target Fusion (MTF). MTF may be a low cost path to fusion, in a regime that is very different from, and intermediate between, magnetic and inertial fusion energy. It requires compression of a magnetized target plasma and consequent heating to fusion relevant conditions inside a converging flux conserver. We will describe FRC's, some of the physics issues, our applications to MTF, and recent data.

The multi-ion species flow onto the plasma boundary has recently begun to attract interest since multi-ion species are often present in practical systems. The ion flow created in the presheath of a weakly ionized He-Ar plasma is studied experimentally. A Modified-Mobility-Limited-Flow (MMLF) model was used to predict ion drift velocities of each species and found to be in agreement with previous LIF measurements [1] for Ar ions 2.0cm from the boundary. The phase velocity of ion acoustic wave was measured by launching a continuous sinusoidal wave, detecting the wave from electron saturation current with a Langmuir probe. The relationship between Ar+ and He+ drift velocities was established by the wave dispersion relation. He+ drift velocities were determined for given Ar+ drift velocities. Ion-ion electrostatic two stream instabilities were observed in the presheath for different positions, partial and total pressures to determine if this instability alters ion drift velocities near the sheath-presheath boundary. The instabilities predicted by fluid and kinetic dispersion relations are compared to the data.

The production of electrons from collisions between charged particles and targets (either solid or gas) is important to problems such as beam transport of heavy ion beams, current avalanche in low voltage diodes, and transmission breakdown in high power waveguides. Collaborators at Tech-X, Lawrence Berkely and Lawrence Livermore Labs are developing a set of easy-to-use computational modules to help model electron production in these systems. In this talk, I'll demonstrate how to use these modules and how I've applied them to study the problems above.

The classical finite-difference time-domain (FDTD) approach to the numerical solution of the time-dependent Maxwell's equations is based on the second order, in space and time, Yee algorithm. However, for an increasing number of applications this algorithm has insufficient accuracy. We replace it by a compact implicit 4th order accuracy scheme that uses the same stencil, but doesn't have drawbacks of the Yee algorithm. A major difficulty with high order methods is the treatment of the dielectric coefficient which is discontinuous across the interface. So we also study the asymptotic and numerical behavior of the solution of the Maxwell equations and the wave equation with discontinuous coefficients in one dimension in both time and frequency space. We present a method for the treatment of the discontinuity that preserves a high order of accuracy for the numerical scheme.

Recent advances in the direct kinetic simulation of fusion plasma turbulence now lay the groundwork and provide an enormous impetus for kinetic closure (using kinetic simulation) of magentohydrodynamic (MHD) computational models. The topic is lively and is still very much an open research area. This is because efficient and practical nonlinear MHD and kinetic methods require subtle underlying orderings, equations and numerical methods (gyrokinetics, gyro-Landau fluid, semi-implicit, finite-element, particle-in-cell, drift-ordering, etc.) all of which must properly meld together into one grand simulation. Even on a particular and well-defined MHD problem, (e.g. internal kink instability, edge- localized modes, tearing modes) knowing whether it is better to use kinetic closure of MHD or solve the problem directly using kinetics is very much unanswered at this point. In this talk we will discuss the possible ways to close MHD equations using kinetics, as well as more direct MHD-like kinetic models. This talk will highlight some recent successes in kinetic-MHD, including modeling of energetic particle effects in fusion plasmas. We will also discuss recent kinetic and kinetic-MHD models of tearing mode behavior.

Magnetic self-organization via Taylor relaxation in a driven plasma underlies the guiding principle of laboratory helicity injection experiments that form spheromaks and the reversed field pinch, and provide non-inductive current drive in a spherical torus. It is also thought to explain the large scale astrophysical magnetic field, for example, in a radio-lobe powered by the accretion disk of a black hole. The critical concept in Taylor relaxation is a linear resonance effect that provides flux amplification. We will first explain the nature of this resonance and its fate when plasma departs from Taylor state. The second part of the talk approaches the same problem by following the dynamics that lead to relaxation. In particular, the so-called instability cascade route to relaxation will be illustrated. Laboratory and astrophysical examples will be drawn upon to appreciate the physical consequences of our analysis.

We analyze single ion motion in a model field-reversed configuration. A two-dimensional effective potential is derived and shown to possess a potential trough as well as isolated critical points. Sufficient conditions for Lyapunov stability are derived for these equilibria and shown to allow large populations of energetically trapped orbits, which can be regular or chaotic. Among these the classical guiding center orbits gyrating about closed field lines form a small minority. Indeed, for moderate field elongation the great majority of trapped orbits appear to be chaotic, with significant populations of regular orbits librating about stable periodic orbits. For larger conserved angular momentum the potential trough disappears and ions are energetically trapped in a larger convex potential well. The dynamics in this regime is very sensitive to elongation, with large resonances and chaotic regions for particular integer values of the inverse elongation. These theoretical results are well confirmed by numerical orbits, Poincare' sections, and Lyapunov exponents. The abundance of periodic orbits and paucity of guiding center orbits suggests that the frequency of the imposed rotating magnetic field in resonant magnetic perturbation (RMP) experiments should be chosen close to the libration frequencies of the dominant periodic orbits rather than the cyclotron frequency.

There are two holy grails regarding the production of charged-particle beams: high brightness and high average current. Both are within reach using the latest accelerator technology. However, conventional design codes based on controlling global moments of the beam provide grossly insufficient intelligence as to the whereabouts of these grails. Consequently, the Beam Physics and Astrophysics Group at Northern Illinois University has been delving into the fundamental physics of space charge. Major topics of investigation have included: chaotic orbits in both time-independent and time-dependent beams, phase mixing and rapid collisionless relaxation, the validity of the Vlasov-Poisson limit, halo formation, and the importance of noise. In short, the lesson learned is that details do matter: the phenomenology of space charge is intricate and involves multiscale dynamics. This talk will present illustrative examples and point to future directions for beam simulation codes.

Modeling a magnetized plasma using single-fluid magenetohydrodynamics (MHD) is inadequate to describe many phenomena. The next simplest model describes the plasma as two fluids, ions and electrons. While this two-fluid model still omits most important kinetic physics, an efficient and accurate numerical treatment of a two-fluid plasma forms the basis for many additional kinetic extensions. Additionally, some examples are given, including the field-reversed configuration and Harris sheet reconnection, where two-fluid calculations would be (or have already been) extremely useful. Next, the problem of efficient numerical solution using time-implicit methods is discussed and contrasted to the single-fluid situation. A uniform, two-fluid plasma supports only real frequency waves, and we seek difference approximations which preserve this feature. The required time differencing is developed and implemented in the NIMROD code, a fusion community-wide finite element code previously applied to single fluid modeling of tokamak and other toroidal plasmas. Results of dispersion tests are discussed and future applications discussed.

The evolution of collisionless and semi-collisional tearing mode instabilities is studied using an electromagnetic gyrokinetic delta-f particle-in-cell simulation model. Drift-kinetic electrons are used. Linear eigenmode analysis is presented for the case of fixed ions and there is excellent agreement with simulation. A double peaked eigenmode structure is seen indicative of a positive Delta-prime. Nonlinear evolution of a magnetic island is studied and the results compare well with existing theory in terms of saturation level and electron bounce oscillations. Electron-ion collisions are included to study the semi-collisional regime. The algebraic growth stage is observed and compares favorably with theory. Nonlinear saturation following the Rutherford regime is observed.

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I will present results from DC breakdown experiments designed to imitate (to some extent) breakdown in superconducting microwave resonators. "Before" and "after" pictures demonstrate the dangers of contaminant particles, and post-breakdown surface analyses show the damage caused by the arc around the field emitter, including the extent of ion bombardment. A simple model can explain the initiation of breakdown at a field emitter around which a monolayer of neutral atoms suddenly desorbs; computer simulations using OOPIC show in more detail how breakdown might be thus triggered, and confirm the model`s predictions of a critical current and gas density necessary for breakdown. Although the source of the gas remains unexplained in most cases, I will present a possible explanation for helium processing of superconducting microwave cavities.

For a radio-frequency sheath, it has been found that the rf sheath dynamics is characterized by the ratio of the rf frequency and the ion transit frequency crossing the sheath. Based on a one-dimensional fluid model, the sheath dynamics in different frequency regimes have been studied by solving the continuity and momentum equations for electrons and ions and Poisson's equation. In this model, the presheath dynamics is taken into account. If the rf frequency is smaller than the ion transit frequency crossing the presheath, the ions in the presheath respond instantaneously to the rf field. Consequently, the ion current entering the sheath is time-varying which affects the sheath dynamics significantly. To investigate the ion kinetic effects, the one-dimensional Vlasov equation for ions is solved by using the cubic interpolated propagation scheme (CIP) while the drift-diffusion model is assumed for electrons. It is found that the ion energy distributions (IEDs) of the kinetic model depend on the ionization term. If the ion production rate is significant in the sheath, multiple peaks of the IED will be formed.

I will discuss the formulation and the properties of the moment implicit particle-in-cell (PIC) method developed at Los Alamos National Laboratory.

The talk will be divided into three parts.

First, I will discus the challenges of multiple scale problems in plasma physics. Plasmas host a variety of processes, often some are of more interest than others. Often the processes of interest are on long space and time scales. The implicit approach is an excellent way to handle this situation. It focuses on the long scales of interest, with proportionate resolution, without needing to resolve smaller scales accurately. The method implicitly averages over the smaller and faster scales. I will discuss the general properties of the implicit method.

Second, I will discuss how the implicit moment method is designed and turned into a computer code. I will summarize the actual formulation we currently use in our CELESTE3D code. I will spend a little more time discussing the most recent advances in this area: the formulation of the Maxwell's equations and the boundary conditions for them.

Lastly, I will discuss some benchmark calculations meant to illustrate the performance of CELESTE3D.

The cooling process and the thermodynamics of an electron plasma are investigated in strongly magnetized limit where the gyroradius of the electron is small compared with the mean interparticle spacing. In the limit, the transfer of longitudinal and transverse energy nearly vanishes. For such a plasma there is effectively an extra thermodynamic parameter, as the longitudinal and transverse energies are independently conserved. As a cooling process, we introduce microwave cooling to the strongly magnetized electron plasma. Unlike ion plasmas, an electron plasma which has no internal degree of freedom cannot be cooled down below a heat bath temperature. However, the longitudinal cooling can be achieved by energy transfer from the poorly cooled longitudinal degree of freedom to the well cooled (by synchrotron radiation) transverse degree of freedom. A microwave tuned to a frequency below the gyrofrequency forces electrons moving towards the microwave to absorb a microwave photon. Simultaneously the electrons move up one in Landau state and then lose their longitudinal momentum. In this process, the longitudinal temperature of the electron plasma can be decreased. On the basis that the transverse temperature is below the Landau temperature of the plasma, we set up two level transition equations and then derive a Fokker-Planck equation from the two level equations. With an aid of a finite element method (FEM) code for the equation, the cooling times for several values of the magnetic field, the microwave cavity, and the relative detuning frequency from the gyrofrequency, are calculated. Consequently, the optimal values of microwave cavity and detuning frequency from the gyrofrequency, for longitudinal cooling of a strongly magnetized electron plasma with microwave bath, have been found. By applying the optimal values with an appropriate microwave intensity, the best cooling can be obtained. For the electron plasma magnetized with 10T, the cooling time to the solid state is approximately 2 hours.

Our goal is to construct a model for the nonlinear saturation of the electron temperature gradient (ETG) instability, which is one possible explanation of observed electron transport in tokamaks. We will present a hamiltonian, in slab geometry, for electron dynamics due to E x B drift and E|| acceleration. We will also present preliminary results of an electron resonant with the ETG mode.

We have measured the heating rate of laser-cooled ions in a Penning trap using Doppler laser spectroscopy and observed evidence of the solid-liquid phase transition. Between 104 and 106, Be+ ions are trapped in a 4.5 Tesla Penning trap and laser-cooled to around 1 mK, where they form a crystalline plasma. This system is a rigorous realization of a one-component plasma. The ion temperature is measured as a function of time after turning off the laser-cooling and a rapid temperature increase is observed as the plasma undergoes the solid-liquid phase transition. We present evidence that this anomalous heating is caused by a sudden release of energy from a non-thermally excited mode of the plasma, presumably the cyclotron mode of heavier-mass ions surrounding the Be+ ions.

The use of nonlinear focusing in particle accelerators has been proposed in a variety of applications. This work proposes and studies yet another application and analyzes the dynamics associated with nonlinear focusing. To begin with, it is proposed that beam halos can be controlled by combining nonlinear focusing and collimation, which is verified by numerical simulations. The study relies on a one dimensional, continuous focusing Particle-in-Cell (PIC) model and a Particle-Core model. Results from the PIC simulations establish the importance of reducing the mismatch of the beam in order to reduce halo formation. It is then shown that nonlinear focusing leads to damping of the beam oscillations thereby reducing the mismatch. This damping is accompanied by emittance growth causing the beam to spread in phase space. To compensate for this, the beam is collimated and further evolution of the beam shows that the halo is not generated. The use of the idealized, one-dimensional, continuous focusing model is justified by analyzing nonlinear alternate gradient focusing systems. The Lie Transform perturbation theory is used to derive an equivalent continuous focusing system for the alternate gradient focusing channel by canonically averaging over the lattice or fast oscillating time scale. The analysis shows the existence of a condition in which the system is azimuthally symmetric in the canonically transformed, slowly oscillating frame. Numerical results show that this condition leads to reduced chaos and improved confinement in the charged particle motion. The Lie Transform analysis is then extended to include space charge effects which enables one to calculate a near equilibrium distribution function which is azimuthally symmetric in the nonlinear lattice.

Using recent theoretical developments concerning the fluid moments of the gyro-averaged Vlasov equation, we have implemented a high-resolution computational model of Alfvén wave propagation. We use full electron and ion gyrofluid equations. This model includes electron inertia and ion pressure terms. We include realistic variations in plasma density, temperature and magnetic field. The resulting profiles feature variations of several orders of magnitude. We study how Alfvén waves propagate from the Earth's magnetosphere into the aurora cusp region of the ionosphere. This model includes a finite electric field parallel to magnetic field lines, and can therefore be used to study the contribution of the Alfvénic disturbances to the acceleration of charged particles. We reproduce the physical phenomena of ionospheric resonance, dispersive electron acceleration, and cold electron burst acceleration. We also study the propagation of Alfvénic disturbances originating from the Io torus into the Jovian ionosphere. The Jovian ionospheric resonator is shown as a possible generator of the observed S-burst radiation emitted from the Io magnetic footprint.

Global studies of magnetically confined plasmas have, up to now, relied primarily on the magentohydrodynamic (MHD) plasma model to study the macroscopic stability and nonlinear dynamics of large plasma systems. It has long been known that basic two-fluid processes, i.e., allowing the electrons and ions to move independently while keeping the set of velocity-moment equations, have important effects on plasma instabilities. Recent developments in computational power and numerics allow two-fluid and other extended MHD models to be used for nonlinear simulation. Results are presented to show that two-fluid effects change the steady state picture and beta limits of a helical-toroidal fusion plasma (the proposed high beta stellarator NCSX), compared to MHD. Magnetic reconnection is enhanced and becomes an important limiting factor in two-fluids. The results explain a number of puzzling experimental observations in stellarators.

The nonlinear dynamics of single ions inside the magnetic field reversed configuration (FRC) were investigated. Due to the high nonlinearity in the equations of motion, the behavior of the system is extremely complex, showing different regimes, depending on the values of the conserved azimuthal angular momentum and the geometry of the fusion vessel. The averaged Hamiltonian was used to study the structure of phase space and find the location of major resonances in the nonlinear regime. The condition for the onset of strong chaos was obtained using Chirikov island overlap criteria. A linear regime was found at higher values of azimuthal angular momenta, where the unperturbed Hamiltonian has a form of two uncoupled simple harmonic oscillators.

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A growing body of experimental data suggests that non-diffusive radial transport of particles can play a major role in the scrape-off layer (SOL) of tokamaks and other machines. This transport may be associated with the propagation of high density plasma filaments or "blobs" that have been observed in experiments with both fast cameras and probes. Theoretical work has shown that these structures propagate to the wall in the presence of an outwards force F and species- dependent F x B drifts. The transport occurs due to different types of forces in both toroidal and linear machines of greatly varying parameters, so the phenomenon is robust and surprisingly universal. The blob theory is qualitatively consistent with the experimental observations of convective transport, spatial and temporal intermittency, and non-Gaussian statistics in the SOL. Convective transport can be especially important for tokamaks because it reduces the efficiency of the divertor and may be related to the observed density limit on some machines. This talk will discuss the experimental motivation for this work, recent progress in theory and modeling, and some remaining unresolved issues.

This fall, Physics 4150, Introduction to Plasma Physics, is being taught with many of the homework problems assigned in Mathcad. The assigned problems are similar to exercises posted online at the course web site, thus the student's work will consist of downloading and modifying the posted Mathcad spreadsheets. For example, an assigned problem to find the potential created by an array of conductors might require only changing the boundary conditions in a spreadsheet that solves Laplace's equation. There are 25 posted exercises which 1) solve Laplace's and Poisson's equation by relaxation (illustrating Debye shielding), 2) plot the trajectories of magnetic field lines from straight wires and loops using Runge-Kutta (illustrating the dipole, x-points, shear, and rotational transform), 3) solve the Lorentz equations of motion for inhomogeneous magnetic fields by Runge-Kutta (illustrating the mirror force and drifts), 4) find the roots of complex dispersion relations using root finders including cases where the waves are growing or damped, 5) illustrate the principal value integral in the plasma dispersion function, 6) perform ray tracing in an inhomogeneous dielectric in the WKB approximation (illustrating ionospheric reflection), 7) illustrate diffusion, mobility and resistivity using equations of motion with Monte Carlo collisions, and 8) illustrate the ponderomotive force by modeling the Paul ion trap.

Unwanted electron emission from metal walls influences the operation of vacuum waveguides. If the electron density becomes large enough, the electron plasma can reflect the electromagnetic waves that are supposed to be transmitted. We have performed numerical simulations of the generation of electrons in high-power vacuum waveguides. In particular, we studied parameters relevant to the high-power waveguides at the Stanford Linear Accelerator Center. An interesting result of our work is ions and neutrals appear to play an important role in the electron emission.

Kinetic plasma simulations based on direct integration of the Vlasov equations are much quieter than corresponding simulations using particle-in-cell (PIC) methods. However, the computational cost of Vlasov simulations in higher dimensions is steep because the Vlasov equations must be solved on a grid of at least 2xD phase-space dimensions where D is the number of spatial dimensions. Fortunately, there are regimes where a full kinetic treatment is required only along one "dominant" spatial coordinate (e.g., the direction of a beam or background magnetic field), with the perpendicular dynamics either suppressed by a strong magnetic field or adequately modeled by fluid-like methods. A hierarchy of hybrid simulation schemes for different levels of particle magnetization will be presented. Examples from simulations of current-driven double layers and electron holes in the auroral ionosphere will be used to illustrate the various numerical approaches.

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This talk will describe results of our on-going studies of the temperature and heating rate of trapped and laser-cooled Be+ ions. These studies are mainly motivated by the possibility of producing entangled states of many ions, which could have applications in quantum information processing and possibly lead to an improved microwave frequency standard. In a Penning trap, charged particles are confined by a combination of static electric fields and a uniform magnetic field. Up to ~1 million Be+ ions are trapped in the NIST Penning trap. When laser-cooled down to temperatures below ~10 mK, the trapped ions form a spheroidally shaped crystal with an inter-particle spacing on the order of 20 micron. The temperature of this system can be measured by laser spectroscopy on a single-photon transition in the Be+ ion. We have studied the heating of the ion cloud after that the cooling laser is turned off. We observe a slow increase in the ion temperature from 1 mK to ~10 mK in typically 0.1s followed by a very rapid increase to ~1 K in another 0.1s. Possible heating mechanisms will be discussed and their relative importance assessed. I will argue that the very rapid temperature increase can be attributed to a solid to liquid phase transition.

VORPAL is an object-oriented multi-dimensional plasma analysis code written in C++. It can handle both relativistic and non-relativistic plasmas using PIC or fluid models. Dynamic load balancing enables it to optimize its performance in parallel by periodically adjusting a simulation's decomposition at runtime. In this talk I will discuss the work that went into implementing a dynamic load balancing solution for VORPAL and how VORPAL's flexible framework made such a task feasible. Performance issues as well as overall results of the design will be addressed.

The Alfvén wave dominated auroral region has been identified as the region near the open-closed magnetic field line boundary where particle acceleration is dominated by waves rather than by quasi- static potential structures found in the upward (with respect to the Earth) and downward current regions. Various models have been considered to explain the acceleration of electrons by Alfvén waves in the nightside auroral region. I will present the characteristics of the Alfvénic auroral region. A linear 1-D gyrofluid simulation [Jones and Parker, 2003] is applied on a dayside auroral field line. A test particle code is used to simulate two electron populations under the influences of Alfvén waves obtained by the gyrofluid code. The electron distributions obtained from the simulation will be compared with observations from the FAST spacecraft.

A new numerical algorithm that encompasses both the delta-f particle-in-cell (PIC) method and a continuum similar to Denavit's "hybrid'' method has been analyzed using a new interpolation schemes. The basic algorithm is essentially a variant of the delta-f method. Briefly, the algorithm is the following: 1) load particles (or characteristics) on a uniform lattice in phase space. The loading need not be uniform, but it greatly simplifies the algorithm, 2) advance the characteristics M time steps, using the usual delta-f PIC algorithm which involves a grid interpolation, deposition, then field solve all on a spatial grid only, 3) every M time steps, deposit delta-f on a higher-dimensional phase space grid, then reset the particle phase space coordinates back to their initial value on the phase space lattice. Also, reset the particle value of delta-f to the phase space grid value. As M goes to infinity, one recovers the usual delta-f PIC algorithm with a somewhat peculiar uniform loading of particles. For M=1 the algorithm is similar to the Vlasov method of Cheng and Knorr. Any value of M={1,2,3,...} is permissible. A quadratic weighting interpolation scheme is implemented \cite{HE}for a small $(k_\perp \rho_i)^2$ two-dimensional bounded slab model, where the phase space is (x,y,v_parallel). The ion-temperature-gradient instability is studied assuming adiabatic electrons and gyrokinetic ions. We will present results with both linear and quadratic interpolation. We will calculate the effective phase space diffusion by such a repeated interpolation and compare with simulation results.

A new electromagnetic kinetic electron simulation model that uses a generalized split-weight scheme and a parallel canonical momentum formulation has been developed in three-dimensional toroidal flux-tube geometry. The long-standing problem in the simulation of kinetic electrons with finite-beta effects, associated with the electron current of the zero-order distribution (Maxwellian in terms of parallel canonical momentum), is solved by evaluating this current using the same marker particles and the same particle shape as that used for the perturbed distribution. The model also includes electron-ion collisional effects and has been linearly benchmarked with continuum codes. It is found that for H-mode parameters, the nonadiabatic effects of kinetic electrons increase linear growth rates of the Ion-Temperature-Gradien-Driven (ITG) modes, mainly due to trapped-electron drive. The ion heat transport is also increased from that obtained with adiabatic electrons. The linear behavior of the zonal flow is not significantly affected by kinetic electrons. The ion heat transport decreases to below the adiabatic electron level when finite plasma beta is included due to finite-beta stabilization of the ITG modes.

A large part of the expense associated with fusion experiments is due to the uncertainties in the dynamics of the plasma. These dynamics lead to instabilities that can spontaneously erupt and degrade the confinement properties of a plasma and sometimes lead to catastrophic disruptions of the entire plasma itself. These instabilities occur in a broad range of spatial and temporal scales, spanning many orders of magnitude, often resulting from nonlinear interactions. Computational simulations are crucial to understanding these phenomena. This thesis research focuses on the numeric study of kinetic effects on magnetohydrodynamic (MHD) instabilities in fusion plasmas. The significant achievement of this thesis work was the implementation of the delta-f particle-in-cell (PIC) simulation in a general geometry, massively parallel, Lagrange-type finite element based, MHD simulation. This hybrid models captures kinetic effects that are not possible to simulate with a fluid MHD simulation alone. The use of the finite element method (FEM) allow the flexibility of modeling the realistic geometries of fusion devices. However, the irregularity of the simulation grid does not allow for conventional (PIC) coupling to the fluid elements represented by the finite element grid. Particular problems resolved include determining where the particle is in the grid, how to 'gather' the field to the particles, how to 'scatter' the particle effects onto the grid, and implementing in a massively parallel framework compatible with the MHD simulation. The addition of kinetic particle effects captures wave-particle interactions important in the saturation or excitation of various MHD instabilities such as the internal kink mode, sawtooth, and fish bone instabilities. We assume that the kinetic particles are an energetic minority species, i.e. kinetic particle density is small compared to the bulk plasma density but the kinetic particle pressure is comparable to the bulk plasma pressure. The kinetic particles are evolved in the MHD fields using the drift kinetic equations of motion. A pressure tensor is calculated from velocity moments of the kinetic particles. This hot particle pressure tensor is added to the MHD momentum equation forming the hybrid kinetic model. This hybrid kinetic-MHD technique lays the foundations for future work in a kinetic closure to the MHD equations.

A heavy ion beam probe has been used to measure density and electric potential fluctuations and the equilibrium electric potential in the core region (r/a = 0.3 to 0.6) of the Madison Symmetric Torus reversed field pinch. This is the first measurement of potential and potential fluctuations in a hot reversed field pinch plasma. In standard plasmas, the equilibrium potential is positive and 1 to 2 kV above machine ground with electric fields strengths of 0.7 to 3 kV/m. Plasmas with low flow velocities due to locking have much lower potentials and electric fields. The potential is inversely related to the density and the electric field is consistent with expectations from the ion momentum balance equation. The observed fluctuations consist of 3 components, a potential fluctuation with f < 10 kHz that is believed to be due to m=0 electric field fluctuations at the edge, density and potential fluctuations at f ~ 15 kHz that are coherent with the dominant m=1, n=6 magnetic fluctuations, and broadband density and potential fluctuations between 30 and 100 kHz. The ExB particle transport due to these fluctuations is much smaller than the total particle transport in a standard plasma.

This talk will begin with a brief introduction to Lie Transform perturbation theory and its use in averaging over small time scales. This is achieved by canonically transforming to slowly oscillating variables. The theory will be applied to a periodic focusing system, that is, a harmonic oscillator with a rapidly oscillating potential. This will be followed by a comparison with numerical results. After this, the theory will be applied to the dynamics of a charged particle in an accelerator with nonlinear focusing. The analysis yields a condition that improves integrability and minimizes chaos in such a system. This will be confirmed by numerical results.

In the optics of charged particle beams, circular transverse modes can be introduced; they provide an adequate basis for rotation-invariant transformations. A group of these transformations is shown to be identical to a group of the canonical angular momentum preserving mappings.

These mappings and the circular modes are parametrized similar to the Courant-Snyder forms for the conventional uncoupled, or planar, case. The planar-to-circular and reverse transformers (beam adapters) are introduced; their implementation on the basis of skew quadrupole blocks is described. Applications of the planar-to-circular, circular-to-planar and circular-to-circular transformers are discussed. A range of applications includes round beams at the interaction region of circular colliders, flat beams for linear colliders and relativistic electron cooling.

The dynamics of fusion plasmas lead to instabilities that can spontaneously erupt and degrade confinement and sometimes lead to catastrophic disruptions of the entire plasma itself. These instabilities occur in a broad range of spatial and temporal scales, spanning many orders of magnitude, often resulting from nonlinear interactions. Computational simulations are crucial to understanding these phenomena.

NIMROD(NonIdeal MHD with Rotation - Open Discussion) is a massively parallel three dimensional magnetohydrodynamic simulation utilizing finite elements (FE) to represent the poloidal plane and a fourier decomposition in the toroidal direction. The use of finite elements allows flexibility in the representation of the simulation domain. The ability to model experimental shots with NIMROD provides a platform to test new ideas of plasma behavior. To expand the physics capabilities of NIMROD, kinetic effects have been added to NIMROD by the addition of delta-f particle-in-cell (PIC) module. The addition of kinetic particle effects captures essential wave-particle interactions important in the saturation of various magentohydrodynamic (MHD) instabilities such as the internal kink mode, sawtooth and fishbone instabilities, and toroidal Alfvén eigenmodes. Particle simulation capabilities in NIMROD can also be extended to simulate various phenomena such as neutral beam injection, ion cyclotron resonance heating, and anomalous los mechanisms. In addition, this hybrid kinetic-MHD technique lays the foundations for a kinetic closure to the MHD equations.

This talk will briefly introduce NIMROD and delta-f PIC in general, then detail the development of PIC in finite elements and their implementation and some preliminary results.

Alfvén waves are ubiquitous in space plasma physics, present in field line bending, during magnetic reconnection, and magnetized shock formation. However, due to their typically long wavelength, comparatively few basic laboratory studies have been made of these waves. Experiments must either be long or dense to accommodate several aflvén wavelengths. At New Mexico Tech we use a high-density helicon generated background plasma to study Alfvén waves under a steady-state current-free conditions. A summary of early studies of Alfvén waves will be presented, as well as our recent results on Alfvén propagation in plasmas with a varying neutral fraction.

Stray electrons are suspected of limiting the performance of many of today's ion accelerators. One source of these electrons is the electrons produced when halo beam ions strike the beam pipe walls. I will discuss computer models developed to help understand this process. In particular, I will discuss this effect as it applies to heavy ion fusion experiments at Lawrence Berkeley National Laboratory. I will show that one can expect as many as 1000 electrons to result from each ion collision and what researchers can do to mitigate the problem.

There are a few key obstacles standing in the way of achieving thermonuclear ignition at the National Ignition Facility (NIF). One of them is controlling parametric instabilities, especially Stimulated Raman Scattering (SRS), where the light wave decays into a scattered light wave and an electrostatic plasma wave (EPW). Parametric instabilities can spoil laser power coupling into the target, and can accelerate electrons which preheat the target. The linear-theory thresholds for significant SRS activity are routinely exceeded in experiments on ignition-relevant quasi-homogeneous plasmas. Experimental results from existing lasers make it clear that SRS saturates via non-linear processes. One possible saturation mechanism for SRS is coupling of energy from the SRS daughter EPW to other non-resonant EPWs [Baker et al., PRL 77 (1996) 67]. If the amplitude of the daughter SRS EPW is large enough, it can decay into a counter-propagating EPW and an ion acoustic wave (IAW), i.e., the Langmuir Decay Instability (LDI). Damping of all these waves ultimately saturates SRS. Another possible saturation mechanism is electron trapping by the SRS EPW. On the one hand, the process greatly reduces collisionless EPW damping from classical levels, promoting instability growth above linear theory predictions. On the other hand, the trapped electrons dynamically detune the EPW, and SRS saturates as a result [H.X. Vu et al., Phys. Plasmas 9, 1745 (2002)]. Theoretical considerations indicate that the dominant saturation mechanism should transition from the former to the latter at some value of the Debye length. Whether this theoretical framework is correct, and whether we can quantitatively predict the transition is a key question, and will help lead to a quantitative, predictive understanding of SRS.

Owing to the large areas and high plasma densities found in some recently developed devices, electrostatic theories of plasma resonances and surface wave propagation [1-2] are suspect as the size of the device is much larger than the free space wavelength associated with the peak plasma frequency. Accordingly, an electromagnetic model of surface wave propagation has been developed appropriate for large area plasmas. The predicted wave dispersion of the two models differs for extremely long wavelengths but is degenerate in devices small compared with wavelength. First principles particle-in-cell (PIC) simulations have been conducted which support these results. Given the slow wave character and boundary localized fields of surface waves, a periodic electrode may be used to resonantly excite a strong wave-particle interaction between surface waves and electrons. At saturation, the electron velocity distribution is enhanced above the phase velocity of the applied wave and suppressed below. The use of this technique (''Landau resonant heating'') to selectively heat the electron high energy tail to enhance electron-impact ionization is demonstrated using PIC simulation. A number of techniques to accelerate PIC simulations in this demanding regime were developed; without them, this research would not have been possible. An implicit method of solving the Maxwell equations which allows extremely high mesh Courant numbers (>100) which still retains the effects of displacement current (critical for these waves) was developed. Also, techniques to eliminate memory thrashing inherent in PIC methods were devised. These made it possible to run these large simulations (using ~30M particles) on a Pentium II 400 desktop.

[1] Nickel, Parker, Gould. Phys. Fluids. 7:1489. 1964.

[2] Cooperberg. Phys. Plasmas. 5, No. 4, April 1998.

In this talk I am going to present how to use the OpenDX package to visualize data stored in files of the HDF5 format. Beside giving an introduction to OpenDX and HDF5, two OpenDX modules (extensions) are going to be demonstrated, which have been developed at CIPS. They import HDF5 data about fields and particles into OpenDX. Moreover, I am going to outline both the usage of the two modules in the context of the Vorpal package and the design basics of OpenDX modules.

The cooling process and the thermodynamics of an electron plasma are investigated in strongly magnetized limit where the gyroradius of the electron is small compared with the mean interparticle spacing. In the limit, the transfer of longitudinal and transverse energy nearly vanishes. For such a plasma there is effectively an extra thermodynamic parameter, as the longitudinal and transverse energies are independently conserved. As a cooling process, we introduce microwave cooling to the strongly magnetized electron plasma. Unlike ion plasmas, an electron plasma which has no internal degree of freedom cannot be cooled down below a heat bath temperature. However, the longitudinal cooling can be achieved by energy transfer from the poorly cooled longitudinal degree of freedom to the well cooled (by synchrotron radiation) transverse degree of freedom. A microwave tuned to a frequency below the gyrofrequency forces electrons moving towards the microwave to absorb a microwave photon. Simultaneously the electrons move up one in Landau state and then lose their longitudinal momentum. In this process, the longitudinal temperature of the electron plasma can be decreased. On the basis that the transverse temperature is below the Landau temperature of the plasma, we set up two level transition equations and then derive a Fokker-Planck equation from the two level equations. With an aid of a finite element method (FEM) code for the equation, the cooling times for several values of the magnetic field, the microwave cavity, and the relative detuning frequency from the gyrofrequency, are calculated. Consequently, the optimal values of microwave cavity and detuning frequency from the gyrofrequency, for longitudinal cooling of a strongly magnetized electron plasma with microwave bath, have been found. By applying the optimal values with an appropriate microwave intensity, the best cooling can be obtained. For the electron plasma magnetized with 10T, the cooling time to the solid state is approximately 2 hours.

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Notions from information theory are applied to the venerable two-dimensional Ising model. A few intensive quantities are examined, the entropy density, or entropy per spin, and the information density, or information per spin stored by the system at a given instant of time. It is shown that the entropy per spin is observable, in the sense that it can readily be measured from the ensemble of patterns generated by a simulation. Just as the magnetization can be measured from statistics over a single spin, the entropy can be measured by considering only the local statistics over a unit square. This result can be generalized to higher dimensions, and other spin systems. The information per spin is the difference between the entropy of a single spin considered in isolation, and the entropy per spin of the pattern as a whole. This quantity has a sharp maximum at the phase transition. The possible usefulness of these notions to the study of nonlinear partial differential equations (PDEs) will be discussed. Time permitting, a number of real-time computer simulations of example nonlinear systems will be demonstrated.

In many applications involving intense beams, it is imperative to be able to limit the non-equilibrium fraction of the beam that may reside far from the core of the distribution known as the beam halo. This aspect of the beam propagation has been notoriously difficult to predict, however recent progress has been made with the development of the so-called particle-core model. Since no direct verification of this model had been undertaken to date, we have carried out a precision experiment to measure halo generation associated with the transport of an intense proton beam through a linear transport channel. The LEDA RFQ was used to inject a 6.7 MeV 10-100 mA beam into a 52-quadrupole channel. Four matching quads at the input of this transport line were used to generate specific mismatch oscillations and the resulting beam profiles were measured at downstream locations over a very wide dynamic range. The results of these experiments tend to support the particle-core model and the significance of controlling mismatch oscillations in minimizing beam halo. However, some anomalous behavior has been observed which has not yet been explained by existing models. An overview of the halo generation process will be given followed by a detailed description of the experimental results.

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Remarkably, a magnetized pure electron plasma can behave like an ideal two-dimensional fluid. Recently, such plasmas have been used to study the dynamics of two-dimensional vortices in a cloud of background vorticity. Experiments have shown that background vorticity can cool a chaotic system of intense vortices into a crystal equilibrium. Further experiments have shown that weak vortices tend to migrate to extrema of the background vorticity distribution. New theories have emerged to explain the experimental observations. In this talk, I will summarize the experiments and related theories, and show that they compare favorably.

High performance has been achieved in DIII-D and in many other tokamaks operating in advanced (AT) modes that exhibit high confinement, negative central shear (NCS), and/or internal transport barriers. A critical issue for sustaining high performance NCS discharges is the ability to maintain current distributions with an off axis maximum. Sustaining such hollow current profiles in steady state requires the use of non-inductively driven current sources. On the DIII-D experiment, a combination of neutral beam current drive (NBCD) and bootstrap current have been used to create transient NCS discharges. The electron cyclotron heating (ECH) and current drive (ECCD) system has recently been upgraded from three gyrotrons to six to provide 5MW of power in long-pulse operation to help sustain the required off-axis current drive. To investigate the effectiveness of the EC system and to explore operating scenarios to sustain these discharges, we use time-dependent simulations of the equilibrium, transport and stability. We explore methods to directly alter the safety factor profile, q, through direct current drive or by localized electron heating to modify the bootstrap current profile. Time dependent simulations using a gyro-Bohm-based model for the thermal conductivity indicate the ability to maintain the necessary q profile for several hundred energy confinement times. We will present details of these simulations exploring parametric dependencies of the heating, current drive, and profiles that affect our ability to sustain stable discharges.

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At NIST we confine 104 to 106 Be+ ions in a Penning trap and use lasers to cool the ions to T < 10 mK. At these extremely low temperatures the ions form Coulomb liquids or crystals and provide an excellent laboratory system in which to study strongly-coupled plasmas, soft-condensed matter, precision spectroscopy, and quantum computing. In this talk I will focus on studies of modes in these systems, including recent experiments in which wakes are generated by pushing on the crystal with a laser beam.

Intensely charged particle beams can produce a low density "halo" surrounding the core of the beam. The primary cause of this halo is a resonant interaction between individual particles and the core. This is an important issue in various applications of high intensity charged particle beams because halo particles can hit the walls of the accelerator, causing radioactivation. In this presentation we discuss the use of nonlinear focusing as a possible method to control beam halos. Results obtained from a particle-core model and from a one dimensional particle-in-cell simulation will be shown.

Recent observations by the FAST satellite have provided high-time-resolution measurements of three interrelated phenomena in the downward current region of the auroral ionosphere: intense parallel electric fields (e.g. double layers) localized to tens of Debye lengths; drifting localized bipolar field structures interpreted in terms of electron phase-space holes; and intense quasi-electrostatic whistler emissions (VLF saucers) originating on the same field lines as the bipolar structures. Numerical simulations and theoretical modeling suggest how these observations may be related. 1-D open-boundary Vlasov simulations show that a density depression in an equipotential plasma carrying a field-aligned current can produce a strong localized parallel electric field (i.e., a potential jump) characteristic of a classical double layer. The electrons accelerated by this field interact with a low-velocity population on the high-potential side to produce a series of electron phase space holes propagating away from the potential ramp. Multi-dimensional (magnetized) particle-in-cell (PIC) and Vlasov simulations of the two-stream instability show that electron phase-space holes initially develop coherence perpendicular to B, thus forming "tubes" in phase space. However, these tubes later become unstable due to a resonant interaction of electrostatic whistlers (or lower-hybrid waves) with vibrational modes of the phase-space tubes. The whistler waves generated by this instability may be the source of the observed VLF saucers.

We have developed an object oriented framework for a new plasma physics simulation code, VORPAL. Through the use of recursion and template specialization VORPAL is designed to run in any number of physical dimensions without loss to performance. The dimension of the simulation is set at runtime allowing for a quick run to be done in 2D to get qualitative results, then move to 3D with the same code and nearly the same input file. VORPAL has a fully general 3D domain decomposition with message passing using MPI. This gives the VORPAL the capacity to incorporate load balancing. The VORPAL framework supports multiple models for the both the fields and the particles. Currently a Yee Mesh finite differencing scheme for the electromagnetic fields and a cold fluid representation of the particles are in place. VORPAL also has the moving-window capability for following phenomena, like laser pulse propagation, that move at a given speed. We will present simulations of laser-plasma interactions, in particular the generation of laser wakefields, using VORPAL.

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A primary challenge in plasma physics is understanding how very small, low-frequency turbulent fluctuations cause energy and particle transport. Including electron physics in any detail is quite a challenge in turbulence simulations. Electrons have a very small mass, and move extremely fast relative to the phase velocities of interest, yet their dynamics is still very important. Electrons drive instabilities and the transport of electrons needs to be better understood. Here, we report on recent progress including fully kinetic electrons and their impact on transport.

The Sandia Z machine is the world's most powerful x-ray source, achieving peak powers of over 300 TW. Researchers are using these high-power x-rays for a variety of experiments, with applications to astrophysics, equation-of-state physics, and inertial confinement fusion. This talk will review recent results from these experiments and discuss some of the active areas of research in improving the performance of the Z machine.

Recent measurements on C-MOD and other fusion devices shows that (i) the density and particle flux in the scrape-off-layer (SOL) is intermittent (turbulent) in space and time, and (ii) non-diffusive transport of particles can play a major role in the SOL. The mechanism for this transport is not yet understood. One possible mechanism for fast convective plasma transport in the SOL may be related to the plasma filaments observed in simulations of turbulence and in experiments using fast cameras and probes. Previous work [1] suggested that high density plasma filaments or "blobs" (highly localized perpendicular to B but with extended structure along B) could detach from the bulk plasma, possibly as a result of turbulence, and would propagate to the outer wall due to the curvature-drift induced polarization and the associated ExB radial drift. In this talk the physical arguments of Ref. 1 will be extended by calculations using a two-field (density, potential) fluid model. I will discuss the properties of density and vorticity blobs, the dependence of the SOL density and plasma flux profiles on the size distribution of the blobs, and the role of ionization. Relevance to experiments will also be discussed.

Work in collaboration with J. R. Myra (Lodestar) and S. I. Krasheninnikov (UCSD)

Branch prediction and speculative execution consist of making probabilistic predictions about the likely near-term evolution of the near-Earth space, and distributing among the cluster machines simulations that assume each of the probabilistically predicted outcomes as initial conditions. As the near-Earth space evolves and real-time satellite data get assimilated into the algorithm, some of the speculatively executed simulations will be proved wrong. At that point the machines that were executing them will be reassigned either to new lines of speculative simulation, or to increase the processing power devoted to more promising simulations already executing. Branch prediction and speculative execution have been very successful in the design of microprocessors, allowing CPUs to attain average processing speeds much higher than linear code execution would permit. The scheme will be demonstrated using particle simulations to tune the parameters of WINDMI, a low-dimensional nonlinear dynamical model of the coupled Magnetosphere-Ionosphere system. Upgrading the scheme to be used with more demanding 3D magnetohydrodynamic (MHD) simulations will also be discussed.

I will describe my efforts in trying to understand some features of the interaction mechanisms in dusty plasmas. Two aspects will be discussed.

First, microscopic processes will be considered. Over the last few years, I have developed several simulation techniques implemented in computer codes and I have developed mathematical physics models for studying fundamental processes in dusty plasmas. I will briefly overview these efforts. The main focus of the presentation will be the results obtained in using such techniques to understand the presence of attractive forces in dusty plasmas. Attractive forces are believed to be responsible for some lattice structures observed in dusty plasma crystals as well as for some coagulation processes. Two mechanisms will be presented, discussed and analyzed quantitatively using simulation methods: plasma wakes and dipole moments induced by asymmetric charging in flowing plasmas (found in space and at the edge of sheaths in glow).

Second, global collective effects will be discussed. The simulation techniques used here differ profoundly to those considered above. Monte Carlo and Molecular Dynamics methods will be presented and applied to study macroscopic effects and transitions of state in complex fluids and in complex plasmas.

Wires carrying high (megaAmpere) currents are suspected of having a thin, hot, ionized corona surrounding a cooler, more dense core region. The details of how these wires behave is important to high-power, wire array z-pinch x-ray sources such as Sandia's Z machine. We model these wires as a Bennett equilibrium with a skin current and radially increasing temperature profile. Using the ALEGRA-MHD code developed at Sandia, we investigate the m=0 linear growth rates for this profile and compare them to growth rates for a low-current (constant current density and temperature) wire.

The current perturbation associated with magnetic reconnection has been measured in the Madison Symmetric Torus (MST). A reversed field pinch plasma configuration such as MST normally exhibits strong magnetic field fluctuations due to tearing modes. Large amplitude, highly spatially localized perturbations in the parallel current density are expected to occur in the region of the reconnection. One such region, the reversal surface, is in the plasma edge. This region was accessed using a pair of insertable probes, each with Rogowskii coils and magnetic coils. The current perturbation's radial structure is broad, comparable to the expected island width, rather than highly localized. The magnetic fluctuation driven radial charge flux due to these perturbations was also measured. This charge flux is proportional to the flux surface average of the product of the parallel current density perturbation and the radial magnetic field perturbation. The measured charge flux, considered as a difference between ion and electron fluxes, is small compared to the total particle flux.

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Solar flares, the reconnection-mediated release of magnetic energy stored in the coronal magnetic field, are physical phenomena of great interest in and of themselves, as well as for their geomagnetic consequences. In addition, according to a conjecture put forth a little over a decade by E.N. Parker, a population of very common but very small flares (the so-called nanoflares) might be responsible for coronal heating. In this talk I will first briefly review the coronal heating problem and Parker's conjecture. I will then discuss a model related to Parker's conjecture, in which flares take the form of an avalanche of small reconnection events in a complex stressed magnetic field driven to a state of self-organized criticality.

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Recent initiatives in space physics have emphasized understanding of solar disturbances and the quantitative prediction of resultant magnetospheric and ionospheric phenomena. These initiatives go under the name of `space weather'. Such quantitative predictions are of practical importance but also test of our understanding of the mechanisms by which the Sun influences the Earth. Solar activity in the form of solar flares, coronal mass injections (CME), and recurrent high speed streams influence Earth's space weather by increasing ionization in the ionosphere and by producing magnetic storms and their associated electrical currents, energetic charged particle injections, and aurora. Of increasing concern as mankind relies more on satellite systems are energetic particles, which can lead to satellite failure through radiation damage. In particular the MeV electrons, also known as `killer electrons', have a deleterious impact on satellite subsystems through deep dielectric discharging. Of special concern is the radiation environment at geostationary orbit where the largest number of satellites is located.

Here I report on a new method of predicting MeV electron fluxes at geostationary orbit 1-2 days in advance using only solar wind measurements. Using this method we have achieved a prediction efficiency of 0.82 and a linear correlation of 0.84 for the two years 1995 and 1996. Using the same model parameters based on the years 1995-1996, the prediction efficiency and the linear correlation for the five year period 1995-1999 are 0.61 and 0.77, respectively. The model is based on the standard radial diffusion equation, which is solved by setting the phase space density larger at the outer boundary than the inner boundary and by making the diffusion coefficient a function of solar wind velocity and interplanetary magnetic field. This model also provides a physical explanation for some observed features of the correlation between the solar wind and the electron flux.

Non-neutral plasmas (e.g. pure-electron plasmas) confined in simple cylindrical traps provide excellent laboratory systems for the study of fluid dynamics and basic plasma transport processes. One such transport process is the viscous transport of particles and angular momentum across magnetic field lines. This type of transport brings about the confined thermal equilibrium state of rigid rotation and nearly uniform density. We have measured the coefficient of viscosity in pure-electron plasmas and find it to be as much as 8 orders of magnitude larger than what is predicted by Boltzmann collisional theory. The enhanced viscosity is due to long range "ExB drift collisions" where particles interact over distances on the order of the Debye length. (Here the Debye length is much larger than the cyclotron radius.) In this talk I will discuss these viscous transport measurements and their implications. In addition, I will provide a partial overview of the experimental and theoretical work done by the Non-neutral plasma group at U.C. San Diego.

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The physics of kinetic electrons and electromagnetic fluctuations are key challenges in microturbulence simulation research. Recently, we have made progress in this area by developing a drift-kinetic electron model using both the split-weight scheme and the canonical parallel momentum formulation of gyrokinetics in a fully nonlinear three-dimensional toroidal field-line-following simulation. This model includes magnetic field perturbations perpendicular to the equilibrium magnetic field. Numerical issues arising from the resolution of the magnetic skin depth currently limit these simulations to small beta and progress in this area will be reported. A complementary hybrid simulation with fully gyrokinetic ions and a zero-inertia electron fluid has been developed as well. The electron fluid equations are derived from moments of the drift kinetic equation and a predictor-corrector scheme for the fluid-hybrid model has been implemented in three-dimensional toroidal field-line-following geometry. This is a much simpler electron model and works well at high beta. We are currently using both models to study the effects of electron dynamics on turbulence, including particle transport (which is zero in simulations using adiabatic response), kinetic Alfvén modes and modification to zonal flows due to kinetic electrons and the generation of zonal fields through including parallel vector potential. Both hybrid and the fully kinetic simulations have been carefully benchmarked with linear theory in the slab limit. Simulation results for turbulence with both trapped-electron drive and ion-temperature-gradient drive will be presented. We will report results including the fluctuation spectra and transport levels (particle and energy) for both the ions and electrons for core H-mode plasma parameters.

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The National Transport Code Collaboration (NTCC) seeks to develop a code for studying anomalous transport in toroidally confined plasma. Much as experimentalists take diagnositics to facilities to study new phenomena experimentally, the NTCC Demonstration Code acts as a computational facility for new models for transport. Theorists must provide their code in the form of an object satisfying certain interface constraints. Having done so, they are in an environment where they may, on-line, check their theory against experiment and run their models with a web-invocable, graphical user interface. The next International Atomic Energy Agency meeting will showcase results from the NTCC Demonstration Code.

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The Department of Pediatrics at the University of Colorado School of Medicine is developing a bank of video cases that correspond to the Pediatric National Curriculum. The cases are used in a WWW/CD-ROM hybrid program with "virtual" Problem-Based Learning (PBL) groups that conduct computer-mediated case discussions between a faculty mentor and students at multiple clinical sites. To the degree possible, our cases simulate a real encounter by using computer-based digital video rather than text, forcing the student to glean the information from the patient encounter and develop the visual recognition skills that are important in pediatric medicine. Unlike most adult patients that can verbally provide a history, pediatric patients very often cannot. Physicians must recognize visual and auditory cues to accurately diagnose a child. Digital video cases also afford the opportunity to model appropriate professional behavior and communication skills. These opportunities are especially important for difficult situations in which the physician needs effective communication skills. Students are often not allowed in some of those interviews and when they are included the variability of the modeling is problematic. Instructional strategies integrate group work, problem solving, and mentoring to support this teaching method. Collaborative learning across the Internet, combined with digital video cases has the potential to have a tremendous impact not only on medical education, but also on distance learning in general.

The invention of the ion trap has led to impressive technological advances in physical measurements as well as the discovery of new states of matter. The motion of ions in the axisymmetric Paul trap has been successfully described by a classical Hamiltonian model, in which the ions move under the combined influence of the focusing radiofrequency (RF) quadrupole field and their mutual Coulomb repulsion. However, most current experiments are carried out in an asymmetric mode, in which the time-averaged "pseudopotential" is a triaxial ellipsoid. Critical points of this potential yield equilibria of ion "crystals", which "melt" to form "clouds". Chaotic motion can lead to enhanced RF heating and loss of ions. We present a classical description of one and two-ion dynamics in an elliptic trap. Stability boundaries for single ion motion are shown to decreased rapidly with increasing asymmetry. The two-ion motion takes place in a fully three-dimensional pseudopotential possessing three isolated critical points known as Morse saddles. Stability is lost when a pair of critical points change type. The results show that global confinement can prevail in the presence of unstable local equilibria. Chaotic motion is studied using four-dimensional surfaces of section.

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Many data analysis problems can be approached by fitting a probability distribution to the data, but there are few models for distributions of images. By a distribution of images we mean a distribution describing images resulting from some process, for example sub-images selected from mammograms by a computer-aided diagnosis system. Previous attempts to model image probabilities either model the probability of some features of the image or are only suited for modeling images of textures; they seem unsuitable for modeling images of more structured objects. To address this problem we formulate a set of models for probability distributions on image spaces, which we call Hierarchical Image Probability or HIP models. They are hierarchical because they explicitly represent image structure at several length scales, and finer scale structures are conditioned on coarser scales. To make the model tractable we factor the distribution over scale and position. Such factoring would make it impossible to capture long-range correlations that arise from the objects being imaged. To fix this we introduce a further hierarchy of hidden variables whose probabilities also factor over scale and position. Since they are unknown, they must be summed over or marginalized to evaluate the image probability, and the summation reintroduces long-range correlations. We present algorithms for performing this sum and for finding the model parameters with maximum likelihood estimation. We have obtained encouraging preliminary results on the problems of detecting various objects in SAR images, target recognition in optical aerial images, and mass detection in mammograms.

This talk demonstrates numerous computer systems that teach physics, chemistry, mathematics, medicine or engineering. These systems have resulted in increased student time on task, improved student grades and reduced faculty costs and are used by more than 4,000 students at over 20 universities.

In physics, we have built an electronic homework system which results in improved test and final exam scores, sometimes adding a full letter grade to the student score. Additionally, the weaker students receive the greatest benefit from this system. In chemistry, Web-based homework program includes thirty-five interactive discovery environments that provide guided inquiry, feedback to student responses and tracking of student performance. Intelligent tutors in chemistry provide levels of customized responses to expose students to the depths of chemical reactions. One tutor enables students to directly manipulate images and work with a palette of tools for placing and moving symbols. Tutors have been tested with over 900 students and show positive improvement in final exams. The electronic homework system provides an open architecture allowing for rapid extensions to new departments.

In addition, engineering tutors provide animated 3D tooling solutions of student designs and advice about relative costs. Evaluation demonstrates that these tutors are as effective as several lectures and homework assignments within a traditional classroom setting. A microbiology tutor provides visual support for an entire undergraduate course in molecular biology with rich 3-D animations depicting production of proteins through the interaction of DNA and RNA. A mathematics tutor uses machine learning to individualize problems and hints.

Each demonstrated project has been evaluated for effectiveness and efficiency. The talk will show how technology's impact on leaning has been quantified and that these systems can be of general use on a national scale.

Results are presented of ALEGRA simulations of the x-ray pulse shape from shot 26 of Sandia's Z machine. ALEGRA is Sandia's multi-dimensional, arbitrary Lagrangian-Eulerian magnetohydrodynamic (MHD) code. Shot 26 produced 180 TW of x-ray power in a 7.5-ns FWHM pulse. This shot was chosen because other MHD codes (MACH II and Darrell Peterson's code from LANL) also have simulated shot 26, thereby providing the opportunity to compare ALEGRA to other codes as well as to data. Discussed in this talk are the effects on x-ray pulse shape of: (i) true void versus plasma fill inside the liner, (ii) differing interface tracking schemes, and (iii) differing levels and models of density perturbations.

Particle acceleration occuring at or near the time of solar flares is common, but it is not so common for high energy particles to reach the Earth's space environment. Solar energetic particles can have very destructive consequences for satellites and astronauts in space; thus, an import question to ask is if a large, destructive proton event will occur in conjuction with a particular solar flare or an associated coronal mass ejection. Acceleration of high energy electrons in flares is generally observed via hard X-ray (bremsstrahlung) and microwave (gyrosychriotron) emissions. In two earlier studies, Kiplinger has found a very high association between an uncommon hard X-ray signature called "progresssive spectral hardening" and interplanetary proton events. Those studies have been been extended from ~330 to more than 700 solar flares observed in hard X-rays by the Solar Maximum Mission (SMM). The results confirm the robustness for the association of progressive spectral hardening with major interplatetary proton events. Some episodes of progressive hardening are also associated with high energy neutrons seen at Earth. Gamma ray lines in flares also result from high energy ion production. A new, ongoing study of all gamma ray line flares seen by SMM compares times of emission of gamma ray lines with occurrences of progressive spectral hardening. These results and their implications will be discussed.

We have examined the photoelectric charging of dust 90-106 microns in diameter dropped through UV illumination and dropped past a UV illuminated surface having a photoelectron sheath. Experiments are performed in a vacuum with illumination from a 1 kW Hg-Xe arc lamp that has a spectrum extending to 200 nm (6.2 eV). We present and compare the photoelectric charging properties of particles composed of zinc, copper, graphite, lunar regolith simulant (JSC-1), and martian regolith simulant (JSC Mars-1). We find that the photoelectric charging properties of the elemental materials are consistent with charging models calculated from the theoretical capacitance and charge on an isolated spherical grain. Dust dropped through UV illumination loses electrons due to photoemission, while dust dropped past an illuminated surface gains electrons from the photoelectron sheath. The photoelectric charging properties of JSC-1 and JSC Mars-1 are more difficult to interpret due to residual charge on the dust. The results suggest that JSC Mars-1 is more susceptible to photoelectric charging than JSC-1. The relation of this work to similar phenomena in the solar system is discussed.

The period doubling bifurcation process in the two-dimensional area preserving mapping is investigated on the basis of symmetry structure analysis. In particular a case of the period-4 orbits in the standard map has been studied thoroughly to analyze boundary islands formation around the principal period-4 island, and the onset of the hyperbolic bifurcation without reflection. It is illustrated explicitly that the hyperbolic bifurcation without reflection gives rise to the birth of twin orbits with the periodicity of the mother orbit.

The effect of poloidally mode coupled, ballooning type electrostatic drift waves on a magnetic island has been studied both analytically and numerically. It has been shown quantitatively that particle orbits become stochastic and their behavior can be a possible candidate for the radial plasma transport across a magnetic island of a tokamak. The transport is significant in that it takes place even when the flux surface is not destroyed. The mechanism of the stochasticity generation is understood as an overlapping of secondary islands caused by resonance between periodic particle motions in the magnetic island and Fourier modes of E x B drift due to the electrostatic drift waves. The diffusion process perpendicular to the island magnetic surface has been shown to follow the Gaussian type and can be influential for the deterioration of the plasma confinement. In addition, local diffusion process in the vicinity of Kolmogorov, Arnold and Moser (KAM) surfaces is discussed.

Finite-length equilibria occur in a number of intense-beam and plasma applications. Penning traps permit the study of intra-beam collective effects, as the additional freedom gained from having an internal conductor permits greater control over the plasma profile, so that monotonic, but not constant, plasma profiles can be obtained. On the basis that the thermal velocity of background neutrals and the drift velocity of the electrons are much lower than the thermal velocity of the electrons, and the rotation frequency is small compared to the gyrofrequency, the equilibrium equation can be reduced to a self-consistent Poisson equation where the source depends on the potential. We solve for these equilibria using a Gauss-Seidel relaxation method. Our results show the shape of the equilibria for various electrode configurations.

In 1985 it was shown that linear analysis techniques were inadequate to describe the behavior of the magnetosphere, and so nonlinear studies of the magnetosphere were begun. When a finite dimension for an attractor was found in magnetospheric data it was thought that conclusive proof was found for chaotic behavior. However, later studies found that random noise with a certain frequency spectrum, called colored random or pink noise, could also give a finite result for the correlation dimension. Since then a controversy has been raging as to whether the magnetospheric was chaotic or stochastic. The definition and method for computing the correlation dimension will be discussed as well as the properties of colored random noise. Also to be discussed is how the properties of colored random noise can lead to a test to determine the difference between a colored random noise time series and a time series from ordinary differential equations that are chaotic.

We study the global stability of charged dust grains orbiting an axisymmetric planet with co-rotating magnetic field. The magnetic field and induced electric field are described in an inertial frame using the magnetic stream function $\Psi$. The combined gravitational, magnetic, and electric forces are modelled by a two dimensional effective potential U^e(\rho,z), parametrized by the conserved angular momentum \pp. The critical points of U^e then locate the equilibrium circular orbits, nonequatorial as well as equatorial. The stable equilibria form the nuclei of potential wells, which can contain large populations of dust grains. These potential wells have their own topological structure, so that a particle which loses local stability can still be trapped globally. Explicit Lyapunov stability boundaries are derived for both positive and negative charges in both prograde and retrograde orbits. Thus, radial stability is lost when a critical point of $U^e$ undergoes a tangent bifurcation, while transverse stability is lost via a pitchfork bifurcation. For a given position near a given planet stability depends only on the charge-to-mass ratio q/m, which for a spherical dust grain is proportion to Phi/a^2, where Phi is the ambient plasma potential and a is the grain radius. The results are applied to Saturn and Jupiter.

The edge and scrape-off-layer (SOL) of a tokamak plasma, while comprising only a few percent of the minor radius, is of great importance in understanding global tokamak confinement and heat deposition on the divertor plates. In this talk, a tutorial introduction to some of the relevant physics governing boundary plasma instabilities and turbulence will be presented, including the use of the collisional fluid Braginskii equations, the role of X-point geometry on wave physics, and the types of modes and instability drives thought to be important. Then, the results of recent work will be presented in which we have identified the curvature-driven resistive X-point mode as the dominant instability of a characteristic L-phase discharge in the DIII-D tokamak. This mode, expected to be a generic L-mode edge/SOL instability, is electromagnetic in the "bad curvature" region, but transitions to an electrostatic mode near the X-point due to the combined effects of resistivity and X-point magnetic shear. Motivated by observations of elevated electron temperature near the X-point, we investigate heating and parallel energy flow induced by the resistive X-point mode. We speculate that energy in the unstable waves flows to and dissipates in the X-point region, heating the electrons. Progress in understanding the nonlinear saturation levels and implications of this mode for perpendicular wave-induced transport will be discussed.

Landau's prescription for determining the dispersion relation of waves in a collisionless plasma with a given velocity distribution for each species lies at the heart of kinetic plasma theory. However, the treatment of damped modes requires the analytic continuation of the distribution functions for complex velocities.

In practical application, velocity distributions are often determined experimentally, or are numerically generated by computer simulations. These general distribution functions cannot be assumed analytic, nor can they necessarily be well-modeled by a superposition of analytic functions (e.g., Maxwellians).

An alternative perspective on the problem of determining the dispersive properties of damped plasma waves will be presented. This method draws a connection between the plasma susceptibility and the convolution (or deconvolution) of the distribution function with simple Lorentzians. This approach lends itself to the numerical determination of the plasma susceptibility for piecewise-analytic distributions that have been subjected to Gaussian smoothing.

The Penning trap confines plasma of electrons (or ions) by using an electrostatic potential to prevent the escape of particles along magnetic field lines. A modified Penning trap has been constructed which has an azimuthal magnetic field made by wires along the axis. The resulting field is helical and particles execute bounce orbits along helical field lines. Drifts cause a particle path in the +z direction to be at a slightly larger radius than in the -z direction so that the orbit is oval, like a rubber band. Collisions cause a step-wise change in position with a characteristic length determined by the width of the oval rather than the Larmor radius. Experiments in the new trap allow aspects of transport theory for toroidal devices to be isolated and tested. The first experiment shows that the transport due to electric mobility scales with the width of the oval drift orbit (the "banana width") and not with the Larmor radius.

Recent advances in available on-board electrical power in satellites has moved plasma propulsion devices from the laboratory to space-based application. In the past year alone more than 80 spacecraft employing some type of plasma propulsion system were flown on commercial vehicles. This talk will present a brief introduction to plasma thrusters including Arcjets, Resisojets, Electrostatic Ion Thrusters, and Magnetoplasmadynamic Thrusters before entering a more detailed analysis of the plasma transport properties in the plume of closed-drift Hall-effect thrusters. The Hall thruster utilizes static crossed electric and magnetic fields to accelerate ionized xenon producing a reactive thrust. The experimental investigation reported utilized in-situ probes to quantify the transport of charged and neutral species in the flowing exhaust plume as well as the construction of a molecular beam mass spectrometer to provide species-dependent measurements of the heavy-particle energy distributions. Among the phenomena discovered was the existence of an anomalous population of ions having apparent acceleration voltages of up to three times that applied to the discharge electrodes. Discussion of such phenomena in the context of charge- and momentum-transfer collisions will be presented.

Numerical, as opposed to symbolic, differential algebras have a growing number of uses in computational science. These differential algebras can be used for simultaneous calculation of some quantity plus a certain number of its derivatives up to some order in some number of variables. Solving a differential equation for a differential algebra element gives the Taylor series expansion for the transfer map - the solution for initial conditions near some particular initial condition. In recent years, it has been recognized that numerical differential algebras are most easily treated by Object Oriented Programming methods in C++, a language that allows operator overloading. In this talk we will review numerical differential algebras and object oriented programming methods. We then discuss the implementation of numerical differential algebras within C++ and show that by judicious choice of data layout, the effiency of the numerical calculations can be increased by an order of magnitude.

The effect of poloidally mode coupled, ballooning type electrostatic drift waves on a magnetic island has been studied both analytically and numerically. It has been shown quantitatively that particle orbits become stochastic and their behavior can be a possible candidate for the radial plasma transport across a magnetic island of a tokamak. The transport is significant in that it takes place even when the flux surface is not destroyed. The mechanism of the stochasticity generation is understood as an overlapping of secondary islands caused by resonance between periodic particle motions in the magnetic island and Fourier modes of E x B drift due to the electrostatic drift waves. The diffusion process perpendicular to the island magnetic surface has been shown to follow the Gaussian type and can be influential for the deterioration of the plasma confinement. In addition, local diffusion process in the vicinity of Kolmogorov, Arnold and Moser (KAM) surfaces is discussed.

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The spatiotemporal evolution of stimulated Brillouin scattering (SBS) in homogeneous plasmas and some aspects of the influence that nonlinear and kinetic effects have on the evolution of SBS were studied.

A one-dimensional analytical linear model based on a fluid description of the plasma was initially developed. It was found that the threshold intensity of the absolute instability and the steady-state spatial growth rate of the convective instability are both independent of the scattering angle. However, the saturation time of the convective instability exhibits a strong inverse dependence on the scattering angle.

The basic model was improved by extending the one-dimensional analysis to include two spatial dimensions and time. In order to assess the effects that the finite size of the laser beam has on SBS, wide and narrow laser-beam geometries were considered. Detailed comparison were made between the predictions of a reduced 1D and 2d models, which can be solved and analytically, and the results of 2D numerical simulations.

The influence that nonlinear and kinetic effects have on SBS was investigated by performing particle-in-cell (PIC) simulations. The results of these PIC simulations were compared against fluid simulations, and good agreement was obtained for sufficiently weak laser intensities. When the laser intensity is sufficiently strong for ion trapping to be significant, PIC and fluid simulations differ substantially. The SBS reflectivity is shown to depend sensitively on the frequency mismatch between the light wave used to seed the instability and the incident laser.

Plasmas, the ionized states of matter, are usually hot and gaseous. However, a sufficiently cold or dense plasma can be liquid or solid. We trap beryllium ions in a Penning trap, and utilize laser cooling to reduce the ion temperature to less than 5 mK. By applying an asymmetric electric field that rotates in the same sense as the ions, we are able to phase-lock the rotation of these plasmas, therefore enabling precise control of the plasma density and shape. The ions freeze into Coulomb crystals, which we have studied through both Bragg diffraction and spatial imaging. The crystals have a rich phase structure, whose features are shared with such diverse systems as neutron star crusts, hard spheres, colloidal suspensions and semiconductor electron bilayers. Plasma modes can be excited with potentials applied to the trap electrodes, and directly imaged by changes in the ion resonance fluorescence produced by Doppler shifts from the coherent velocities of the mode. Enhanced radial transport is observed where modes are resonant with static external perturbations; similarly, the plasma angular momentum can be usefully changed through the deliberate excitation of azimuthally asymmetric modes. Precise control of the plasma's angular momentum and structure is important for possible applications such as frequency standards, quantum computing and antihydrogen production.

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I will briefly review the physics of the saturation of kinetic instabilities due to wave trapping, and the role of collisions in wave-particle resonant interaction. I will provide a general introduction to the delta-f method, then discuss some of the difficulties in extending delta-f method to cases with collisions, and show how the introduction of a convenient tool (the marker distribution in extended phase space) overcomes such difficulties. I will then try to apply the new method to the simulation of a recent Tokamak Fusion Test Reactor Experiment and discuss the result.

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WINDMI is a nonlinear dynamical model for the coupled Solar-Wind--Magnetosphere--Ionosphere system. The model couples the four basic energy components of the nightside magnetotail (lobe magnetic energy, current sheet ExB energy, parallel kinetic energy, and thermal energy) to the ionosphere by the nightside region 1 currents (substorm current wedge). It includes the large ion gyroradius kinetic physics in the quasineutral sheet that converts ExB convection to thermal energy through the chaotic conductivity, and the finite parallel heat flux neglected by magnetohydrodynamics (MHD). The model predicts both the state of the geotail and the ionospheric westward electrojet index from the value of the solar wind speed. In the absence of solar wind driving and ionospheric damping the model conserves energy and is Hamiltonian. With solar wind driving and ionospheric damping, the system is consistent with Kirchhoff's rules expressing the conservation of charge and energy. This ensures that the solar wind input power is divided into physically realizable sub power components, a property not shared by signal processing filters for instance. WINDMI provides a consistent mathematical framework that can be used to investigate different possible scenarios for the evolution of the driven Wind-Magnetosphere-Ionosphere system. We will report on three studies of such models: (1) lobe stored magnetic energy as a function of the interplanetary magnetic field and solar wind dynamic pressure, (2) the role of the nonlinear ionospheric conductivities and (3) the change in dynamics with the nature of the unloading mechanism, as for example the near Earth neutral line.

The most popular theory of solar system formation states that the nine planets accumulated from a disk of gas and dust orbiting the Sun. N-body simulations of the final stages of planet formation from several hundred planetary embryos yield satisfcatory results in the inner solar system, but completely fail to form massive planets in the outer solar system. The problem is that bodies in the outer solar system are weakly bound to the Sun and widely dispersed. Mutual gravitational interactions in the outer solar system produce large velocity dispersions, small collision cross sections, and stalled planetary growth.

A possible solution to this problem is the addition of collective gravitational wave dynamics in the disk. Planetary emryos tend to excite waves in the disk which can strongly damp the velocity dispersion of the larger bodies, leading to larger collision cross sections and more rapid planetary growth. Althought the theory of wave-planet interactions is fairly mature, practical techniques for including wave-planet interactions in N-body simulations remain to be developed. I will discuss a reduced description of wave-planet interactions that is somewhat similar to reduced descriptions of wave-particle interactions that are used in plasma physics simulations. The goal of this talk is to draw useful analogies between the methods of plasma physics and the methods of solar system dynamics and to facilitate the exchange of ideas between these two disciplines of classical physics.

The talk will present experiences with parallelizing and running a 3D gyrokinetic flux tube code on the Origin 2000 at ACL, LANL. The parallelization and performance of the code will be discussed. As introduction, a brief overview of parallel computing will be presented. This will cover some terminology, basic architectures of massively parallel machines, parallel schemes and philosophies, and some MPI.

I will discuss the derivation and results for a one-dimensional gyrofluid model of Alfvén waves in the Magnetosphere. This model is derived from the drift-kinetic equation and it accounts for the effect of a dipole field beta variation. Interesting results include a realistic wave period, and significant electric field fluctuations at the ionosphere-magnetosphere boundary which could contribute to acceleration of auroral electrons.

The Solar Heliosphere Observatory (SOHO) has been the flagship solar observatory of the European Space Agency and NASA since it began service in April, 1996. Its remarkable discoveries and nearly flawless performance for two years induced agencies to grant an extended mission beginning after its first two years. In late June, 1998 within the span of a few hours, the one billion dollar mission started spinning out of control and contact was lost for weeks. It has since been found, communications are restablished, and a painstaking "healing" process is underway that may restore much of the observatory's function.

Substorms are always observed during the main phase of magnetic storms. In the expansion phase of each substorm ions and electrons suddenly appear at synchronous orbit, accelerated by the collapse of the tail-like field. This correlation has led many researchers to believe that storms are a consequence of the ring current produced by the drift of these particles. However, studies of the Dst index which measures the strength of the ring current show that injection occurs before the expansion phase, and that Dst actually decreases in strength at expansion onset. What then is the role of substorms in producing magnetic storms?

A tokamak sawtooth crash phase has been studied numerically. By starting from a concentric equilibrium, it has been shown that the evolution through an m/n=1/1 magnetic island induces secondary high-n ballooning, (Rayleigh-Taylor-like) instabilities. The magnetic island evolution gives rise to convection of the pressure inside the inversion radius and builds up a steep pressure gradient across the island separatrix, or the current sheet, and thereby triggers ballooning instabilities below the threshold for the axisymmetric equilibrium. Due to the onset of secondary ballooning modes, concomitant fine scale vortices and magnetic stochasticity are generated. These effects produce flows across the current sheet, and thereby modify the $ m=1$ driven magnetic reconnection process. The resultant interaction of the high-n ballooning modes with the magnetic reconnection process is discussed.

Ice, being an important substance to our life, possesses unique physical properties which attract attention of many researchers. Some of those properties are poorly understood even today. For instance, formation of a liquid-like layer on the ice surface is mostly unexplained. Other properties like electrical and optical are better studied, though leaving many unsolved questions. In part slow progress is explained by experimental difficulties one encounters trying to work with ice. High vapor pressure, low atomic weight, hydrogen bonding, liquid-like layer and protonic electric conductivity make it very difficult and sometimes impossible effectively apply modern techniques and methods used to study other solids. From the standpoint of the electronic conduction theory, ice, with its wide band gap, E(gap)= 10.9 eV, must be an insulator. However, it exhibits significant electric conductivity ( ~10-7 (Ohm cm)-1 at T = - 10?C), which is protonic by nature. The electric conductivity is explained by the motion of so called defects of protonic subsystem: ions and Bjerrum defects. In total there are four different charge carriers. Practically all properties of ice including mechanical strongly depend on the state of protonic subsystem, concentration of charge carriers and their mutual proportions. The talk will describe the protonic photoconductivity of ice, the photo-plastic effect in ice, and methods used to investigate the nature of photo charge carriers.

No Abstract Available

A time-dependent theoretical model of surface wave induced magnetic reconnection (SWIMR) based on the mathematical analysis of resonant absorption of Alfvén waves near a neutral point is briefly reviewed. Keeping in view recent critical rewiews of vortex-induced magnetic reonnection (VIMR ) it is argued that SWIMR may be a more plausible mechanism to explain the flux transfer events (FTEs) at the magnetopause. It is further suggested that SWIMR may be responsible for the recently observed plasmoid ejections from the microflares in the solar corona.

A linear gyrokinetic system for low frequency electromagnetic modes is developed. A wide range of modes in inhomogeneous plasmas, such as the kink modes, the compressional and shear Alfvén modes, and the drift modes, can be recovered from this system. The inclusion of most of the interesting physical factors into a single framework enables us to look at many familiar modes simultaneously and thus to study the modifications of and the interactions between them in a systematic way. Especially, we are able to investigate selfconsistently the kinetic magnetohydrodynamics (MHD) phenomena entirely from the kinetic side. Phase space Lagrangian Lie perturbation methods and a newly developed computer algebra package for vector analysis in general coordinate system are utilized in the analytical derivation. A two dimensional finite element code has been developed and tested.

I will briefly review the physics of the saturation of kinetic instabilities due to wave trapping, and the role of collisions in wave-particle resonant interaction. I will provide a general introduction to the delta-f method, then discuss some of the difficulties in extending delta-f method to cases with collisions, and show how the introduction of a convenient tool (the marker distribution in extended phase space) overcomes such difficulties. I will then try to apply the new method to the simulation of a recent Tokamak Fusion Test Reactor experiment and discuss the result.

I will discuss numerical solutions of two distinct problems in dynamo theory. The first calculation is kinematic, and investigates the generation of magnetic fields by a horizontally periodic layer of identical hexagons. This flow acts as a dynamo for sufficiently high fluid conductivity, even though it has zero helicity and is purely poloidal. It is integrable, and must therefore be what is termed a slow dynamo (the distinction between fast and slow dynamos will be explained). The second calculation looks at field generation by the chaotic family of ABC flows. These are periodic in all three space directions. Kinematic calculations will be reviewed to illustrate the evidence that these flows yield fast dynamos. New results will be presented which feature the back reaction of the Lorentz. These demonstrate that dynamos with very strong fields are indeed possible, though the examples studied have zero mean field. (The issue of whether or not dynamos can generate fields of the strengths observed in astrophysics is currently contentious.)

Independent observational and theoretical developments have led to the current consensus that the solar dynamo mechanism responsible for the solar cycle is operating in the thin overshoot layer beneath the base of the convection zone. Therefore studying the physical processes involved in the transport of toroidal magnetic flux across the solar convection zone and its emergence as active regions becomes and important part of understanding solar magentic activity. Although investigations based on a one-dimensional thin flux tube model have produced interesting results which explain the origin of some basic observed features of solar active regions, it is a highly simplified picture with severe limitations. Recently, multi-dimensional magnetohydrodynamic (MHD) simulations have been carried out to investigate aspects of the dynamics of emerging magnetic flux tubes that cannot be addressed by the 1-D thin tube model. In this talk we present the results of two-dimensional simulations of the buoyant rise and mutual hydrodynamic interactions of twisted, horizontal flux tubes in a stratified layer representing the solar convection zone.

91��Ƭ�� 50 years ago it became clear, that the Sun is losing mass (and angular momentum) due to a continuous outflow of material: the Solar Wind. The interaction of the Solar Wind with the Earth's magnetosphere sometimes can have an impact on everyday life; the northern lights are the most impressive results of this interaction. To understand the origin and the acceleration of the Solar Wind it is of importance to understand the processes in its source region, namely the solar chromosphere and corona. The physical parameters, e.g. temperature or density, are determined with the help of spectroscopy. Because the relative elemental abundances are crucial for the line ratios, one has to understand the change of the abundances throughout the chromosphere and corona. The abundances may also have an influence on the heating of the solar corona and they can be used as a tool to map the Solar Wind back to the solar photosphere, to locate its source region. The observations show, that elements with a first ionization potential (FIP) below 10eV are enriched compared to those with a higher FIP typically by a factor of 4. An ionization-diffusion mechanism is proposed to understand these observations in a large variety of phenomena, as e.g. slow and fast wind or polar plumes.

Onsager symmetry (symmetry of the off-diagonal coefficients of the transport matrix) is one of the most fundamental properties of any macroscopic system in equilibrium (indeed, it's a classical thermodynamics textbook topic). Nevertheless, it has been an issue of controversy in the plasma community. The core of the argument is the question of symmetry's applicability - originally derived for equilibria - to turbulent conditions. I will review the topic, from the classic equilibrium theory to recent results which extend the validity of Onsager symmetry to the steady-state non-equilibrium (turbulent) situations. The foundation of the symmetry in reversible microscopic dynamics will be discussed. A covariant formulation of the problem will be considered. Special attention will be paid to the cases of Onsager symmetry in tokamak plasma (classicial, neoclassical, and turbulent).

Structure formation in the interplanetary magnetic field is a common feature of collisionless space plasma turbulence. It often occurs in the form of discontinuities, shock-trains, and nonlinear waves. Nonlinear dynamics of high-amplitude (compressible) Alfvén wave trains subject to collisionless (Landau) dissipation is investigated in both "single wave" and turbulent regimes. In beta=1 plasmas (typical for the solar wind), where the traditional DNLS-based approach fails, the effect of resonant particle-wave interactions is shown to lead to the formation of various types of Alfvénic discontinuities (e.g., arc- and S-polarized rotational discontinuities), which are commonly observed in the solar wind in spacecraft observations. In the turbulent regime, two different regimes (or phases) of (compressible) Alfvénic turbulence are predicted. The influence of other kinetic effects (e.g., collisions, gyro-kinetic effects, trapping of particles by a wave) on the wave dynamics is also investigated.

Understanding the velocity distribution of the electrons in Jupiter's Io Plasma Torus is an important consideration when studying the radiation emitted from the plasma and the flow of energy through the system. Torus electrons are known to be much cooler than torus ions (by a factor of roughly 10) because they are efficiently cooled by e-impact radiative collisions with sulfur and oxygen ions. The distribution fe(v) is also known to possess a high-energy tail that is thought to be produced (in part) by interactions with plasma waves. Results from a new kinetic model that includes e-e and e-i coulomb collisions, e-i radiative collisions, as well as plasma wave electron acceleration will be presented, with particular emphasis on understanding the overall energy budget of the Io torus plasma.

Spacecraft frequently measure intense burts of Langmuir waves in conjunction with field aligned electrons in the auroral ionosphere. A numerical simulation model which includes both wave-wave and wave-particle effects has been constructed. This model is based on differential equations, and allows us to examine the evolution of the extremely weak precipitating electron beams observed in the auroral ionosphere. These beams are often difficult to study using conventional particle-in-cell techniques, due to the relatively high noise levels of these simulations. Our model couples the 1-D quasilinear diffusion equation (which evolves the electrons) to the 2-D magnetic Zakharov equations (which evolve the wave spectrum), evolving the electron distribution function and Langmuir wave spectrum self-consistently. Previous self-consistent simulations have been 1-D. Previous 2-D studies have not been self-consistent, assuming either a fixed electron distribution or a fixed wave spectrum. Preliminary results of the new quasilinear-Zakharov model show that wave-wave and wave-particle effects act on similar timescales. Furthermore, forward scattering of Langmuir waves tends to heat the core of the electron distribution. This effect does not occur in 1-D.

Several dusty plasma experiments in progress in the plasma laboratory will be described. 1) The charge on particles dropped through a low-density plasma has been measured and compared with theory. The particles, 20 - 100 microns in diameter, are smaller than the Debye length, and it is confirmed that their charging is described by the orbit-limited theory of Langmuir probes when secondary emission is properly included. These measurements have recently been extended to a granular sample of lunar regolith returned by Apollo 17 astronauts. 2) An instrument developed for detecting charged dust particles is being modified to be flown on a rocket. The rocket instrument will detect charged atmospheric aerosols in the polar mesosphere and is expected to return data on the abundance and charge state of particles in noctilucent clouds. Launch is scheduled for August of 1998. 3) Tabletop projects involving undergraduates include a) observations of dust trapped for 6 or more hours in orbit about a sphere in vacuum with applications in celestial mechanics and b) trapping of clouds of charged droplets in a Paul trap and observations of modes of oscillation relevant to non-neutral plasmas.

The plasma environment in the comet-like tail in the Earth's nightside forms an interesting plasma laboratory for studies of tenuous (density ~1/cc, temperature ~few keV) plasmas. Various observational and theoretical studies have recently suggested that a key element in the growth of large-scale instabilities is the formation of a thin (of the order of ion gyroradius) current sheet within the plasma sheet. The dynamic processes in the magnetotail are manifested in the polar ionospheres as bright auroral displays created by particle precipitation into the upper atmosphere. Thus, the auroral observations provide a projected image of the large-scale magnetospheric processes, which otherwise are difficult to capture due to the vast size of the system. This talk addresses the plasma environment in the nightside magnetotail during magnetospheric substorms. Model results of the thin current sheet formation prior to the auroral breakup are presented, and the stability conditions for the tail are discussed. The auroral observations during substorms are related to the tail processes by magnetic field-aligned mappings.

The mesophere, thermosphere, and ionosphere are highly complex regions of the Earth's atmosphere, with interacting dynamical, chemical, and radiative, and electrical variations that are strongly coupled with the magnetosphere and lower atmosphere. To understand how these coupled systems interact to produce the great variability observed in the upper atmosphere is one of the major problems in space physics today. One tool that has been developed to study this region of the of the atmosphere is the National Center for Atmospheric Research's Thermosphere-Ionosphere-Mesosphere-Electrodynamics General Circulation Model (TIME-GCM) that incorporates many of the aeronomic processes necessary to simulate the structure and dynamics of the region and determine its response to solar and auroral variability. The TIME-GCM has been used to study large-scale thermosphere and ionosphere dynamics and interacting electrodynamics for a variety of geophysical conditions. The results of simulations with the TIME-GCM for both quiet and disturbed geomagnetic will be discussed.

Comets, planetary rings, asteroids, and the Moon are all examples of where dust grains and plasmas coexist. Dust particles collect electrostatic charges and act as sinks or sources for the density, momentum and energy of their plasma environment. I will briefly discuss the most important processes and show examples where dusty plasma theories were successful in explaining the observed spatial distribution of small dust particles.

Spiral density waves arise frequently in astrophysical disks, such as galaxies and protostellar nebulae. We have discovered a new process undergone by these waves, in which they couple and scatter to lower azimuthal mode number. The upshot is that wave energy undergoes downscattering, in which and initial perturbation evolves to an ever more symmetric state. Downscattering offers explanations for several diverse phenomena, such as the prevalence of galaxies with low numbers of arms, the formation of binary stars, and angular momentum transport in star formation. The scattering process is a fluid analogue to nonlinear Landau damping, in which two linear modes exchange energy, via the resonance of their beat mode. This process has been observed in recent laboratory experiments with diocotron modes in a pure electron plasma, which follow similar (not identical) dynamics. In this work, we calculate the scattering rate for a thin fluid disk model using a weak turbulence expansion, and producing an analytical formula for the scattering rate. This formula clearly shows the tendency to scatter to lower azimuthal mode number. This direction of scattering results from the tendency of disks to minimize free energy via inward mass and outward angular momentum transport. We apply the predicted rates to a model galaxy, showing scattering to be a robust mechanism, comparable in magnitude to typical linear growth rates.

The interaction between Jupiter's magnetosphere and its moon, Io, causes strong field aligned currents, and produces intense decametric radio emissions and auroral activity. After the discovery of these radio emissions in 1955, this interaction was believed to involve a steady current flow across Io, induced by Io's orbital motion across Jupiter's magnetic field lines. These currents would flow along the field lines and close through Jupiter's ionosphere. After the Voyager spacecraft observed a dense plasma torus around Io, in 1979, this model seemed unlikely: Based on propagation times and flow velocities, it seemed that the system would not settle into equilibrium. Instead, the interaction would take the form of an Alfvén wave propagating away from Io and towards Jupiter. Now, with the new results of the Galileo spacecraft, our understanding of the Io interaction may change again. In this talk, I will describe the previous theories of the Io interaction, and the time scale arguments that determine whether the interaction is one of steady currents or an Alfvénic disturbance. I will then discuss my own work on the nature of the interaction and how it couples to the high-latitude phenomena. After summarizing the Galileo results, I will present a new model for the interaction, motivated by the Galileo data, and the implications for Jovian radio emissions and aurora.

The importance of magnetic fields in determining the structure, energy balance, and star formation history of galaxies is universally accepted, but the origin and evolution of galactic magnetic fields is still uncertain. I will discuss our current state of knowledge and some unsolved problems.

A grand view of self-organization is constructed from the results of our various simulation studies such as generation of dipole magnetic field (so-called geodynamo), coagulation of fine grains in plasmas, crystallization of polymer chains, solar loops and flares, merging of spheromoks, magnetohydrodynamic self-organization.

The space environment is known to have significant effects upon human technological systems. The broad solar-magnetospheric-ionospheric set of variations having such adverse impacts on human endeavors are called "space weather". In this talk I will present information about a number of the most well-known and well-documented elements of space weather with a focus on satellite operational anomalies. The physical causes of such problems and possible ways of averting problems in the future will also be described. Several recent examples of space weather impacts will be presented including the recent failure of the AT&T Telstar 401 statellite on 11 January 1997.

Recent Thomson scattering Measurements at the Rijnhuizen Tokamak Project (RTP) of the FOM-Institute for plasma physics (The Netherlands) reveal the existence of many hot plasma filaments in the center of an externally heated plasma. These observations break down the old paradigm that describes a Tokamak plasma as a nest of closed magnetic flux surfaces. The plasma filamentation may account for many unexplained transport and confinement properties. The measurements however are very incomplete and leave open many questions on the formation, structure, lifetime and dynamics of the filaments. In this talk I will discuss numerical simulations which model the structure, lifetime, and dynamics of hot plasma filaments in the magnetohydrodynamic (MHD) model, using a two-dimensional resistive MHD code. I will give a brief overview of the filamentation measurements, of the MHD model, and of the finite volume numerical technique which is used. This will be followed by a more extensive discussion of the simulation results.

Three-dimensional kinetic turbulence simulations are producing fluctuation spectra and transport levels similar to experimental results for the first time ever. This has occurred due to developments in reduced equations (gyrokinetic formalism), numerical methods (low-noise delta-f method) and the enormous gains in massively parallel computing. This talk will give an overview of these fairly recent developments.

We produced simultaneously dense and well-confined nonneutral plasmas by spherical focusing. A small (3mm radius) Penning trap has low-energy electrons injected at a single pole of the sphere. Precisely when the trap parameters are adjusted to produce a spherical well, the system self-organizes into a spherical state, through a bootstrapping mechanism which produces a hysteresis. Additional confirmation of the dense spherical focus is provided by electrons scattered by the central core. Core densities up to 35 times the Brillouin density have been inferred from the data.

We have previously proposed a method for reducing chaos in four-dimensional symplectic maps, which describe the motion of charged particles in accelerators. The method relies on solving for parameter values at which the linear stability factors of the map have the values corresponding to integrability. We suggest that this method be applied to accelerator lattices in order to increase the volume of stable region in the phase space. We have now implemented a computational scheme for the practical application of this method to accelerator lattices. The Advanced Light Source (ALS) lattice is used as an example to test this method. Preliminary results show substantial increase of the volume of stable region which implies the validity of the method.

The Earth's magnetotail current sheet has received a significant amount of attention since its discovery, due to its suspected role in the storage and subsequent release of magnetic energy associated with geomagnetic substorms. The weakly magnetized nature of the current sheet region demands that modeling efforts retain the particle physics, so that fluid based models cannot be used to accurately model this region.

We report on the results of simple, 1D particle based equilibrium models of the current sheet. In particular, we discuss the importance of particle stochasticity in determining the gross current sheet structure. We have found that small numbers of stochastic particles can lead to significant thickening of the current sheet, with potential consequences for current sheet instability theories. In addition, the quasi-trapped nature of these particles can lead to force balance failure, so that in certain parameter regimes (particulary in the near Earth, dipolar region) thin, 1D current sheet solutions do not exist.

Various Models of the Parametric Decay Instability (PDI) try to address the effects of plasma inhomogeneity and nonlinearity simultaneously in order to assess the evolution of this instability in ionospheric and laser produced plasmas. David Newman and I have been cooperating on developing analytical and numerical schemes which can attack these issues from various mutually complementary points of view. This seminar will report on the progress we have made so far including comparisons between our various results. A discussion of our plans for future work will also be presented. In the context of laser plasma interactions, there is great interest in reduced descriptions that capture the macroscopic physics on length and time scales of interest. PDI (Parametric Decay Instability), OTSI (Oscillating Two Stream Instability) and related phenomena at or near the critcal density are excellent testbeds for the study of all parametric instabilities which involve nonlinear interactions between plasma modes. Secondary decay processes, Zakharovia and beyond are the pressing issues waiting to be tackled.

A new computational tool for plasma physics research is being developed with support from the Office of Fusion Energy. The purpose of the project is twofold. First, there is a need for improved modeling of low-frequency behavior in tokamaks, where a soft beta limit has been observed to inhibit experimental performance. Second, the project itself is an experiment in modern code development. The team uses concurrent engineering with Quality Function Deployment to direct and coordinate developers who are scattered across the U.S. Technical highlights include a general two-fluid formulation that retains all terms in the cold ion and electron momentum density equations. An implicit Ampere's law ensures numerical stability at large time-steps, though the equations support high-frequency normal modes at small time-steps. Energy equations for the two species are advanced separately with semi-implicit operators to stabalize high wavenumber sound waves, and a variety of closure schemes may be used. The spatial representation features finite element discretization in the poloidal plane and Fourier components in the toroidal direction. This will permit efficient modeling of complicated experimental cross sections for a variety of experiments.

No abstract available

Non-neutral plasmas contain charges with only one sign, and are typically confined by static electric and magnetic fields in Penning traps. Except for a global cross-field rotation, these plasmas follow the dynamics of One Component Plasmas and are unique in that they can relax to global thermal equilibrium while confined, allowing incisive quantitative measurements of fundamental processes for direct comparison with theories. I will give a brief introduction to the subject and then concentrate on the National Institute of Standards and Technology experiment using laser-cooled Be+ plasmas and crystals. Here, we have been able to stabilize and control the global ExB rotation of up to 10^6 Be+ ions with an externally applied electric asymmetry rotating in the same direction as the ions. Laser induced flourescent images show that the aspect ratio of these steady-state spheroidal plasmas, which determines the equilibrium density and rotation frequency, can be varied by gradually changing the frequency of the external drive. Furthermore, accurate photon correlation measurements on Bragg scattering patterns from crystals indicate that the lattice structure can be stable for long periods of time (up to one hour), and they can be precisely phase locked to the applied field without any slip. This technique enables precise control of the plasma properties which is important for trapped ion frequency standards, and may also be utilized in other Penning trap experiments such as the syntheses of antihydrogen.

The interaction of ultra-short, high-intensity pulses with gas targets is a field of growing interest. Highly-ionized atmospheric-density plasmas are a potential source of coherent VUV and X-Ray light, as well as a potential source for charged-particle acceleration. Creation of such plasmas via ionization by intense, femtosecond pulses holds promise for the precise control of the initial plasma conditions which are critical to these applications. We have developed a technique for measuring atomic ionization rates in the presence of high-intensity laser light based on the direct measurement of the phase change of an optical pulse. Knowledge of these rates is important in many areas of strong-field physics, most notably in the laser-fusion arena. We use this technique to study the ionization dynamics of atmospheric-pressure noble gasses interacting with high-intensity femtosecond laser pulses.

Low-altitude particle precipitation in the ionosphere provides and important measurement of the distant magnetospheric regions that are connected to the ionosphere by the magnetic field. From spacecraft measurements at high latitudes in the dayside ionosphere we are able to investigate the distant magnetopause, including the effects of magnetic reconnection. In the nightside ionosphere we are able to investigate the distant plasma sheet extending from the Earth to a downtail reconnection site, and to study its temporal and spatial variability. This presentation will illustrate the low-altitude particle signatures of the magnetospheric source regions, and describe techniques used to provide quantitative estimates of the processes occuring in these distant regions, including particle energization near the distant magnetotail reconnection site and in the tail current sheet.

I will present a new magnetic configuration for plasma confinement. I will explain why it is new and why it has a better confinement. This system turns out to be omnigenous (meaning that the radial displacement of particle orbits is zero on average) and far from being quasihelical.

The electrojet as in ionospheric current strong enough to deflect a compass needle. This current flows along the Earth's magnetic equator and in the auroral ionosphere within the E-Region (90 - 120 km in altitude). Two plasma instabilities disrupt the flow of the electrojet current: the modified two-stream (Farley-Buneman) and the gradient-drift instabilities. I shall argue that both these instabilities nonlinearly drive D.C. currents in the E-Region ionosphere. These currents flow parallel to, and with a comparable magnitude to, the fundamental Pederson current. Hence, wave-driven currents act to discharge the electrojet, effectively reducing the resistivity of the E-Region. This talk will review the physics of E-Region waves, show a number of results from simulations of the two-stream instability, describe the nonlinear behavior leading to DC currents, and discuss a few implications of this nonlinear current.

A destabilization of thin current sheets in the near-Earth's magnetotail was suggested to cause the onset of magnetospheric substorms and reconnection in space plasma in general. Current instabilities as well as two-dimensional tearing instabilities were supposed to be the physical mechanism of this process. Unfortunately, neither did the possible current instabilities appear to provide enough "anomalous" resistivity nor did the two-dimensional tearing mode prove to grow for typical initial current sheet configurations. Considering the current sheet in three dimensions fully kinetically we have now obtained the conditions for the current sheet destabilization. They appear to be essentially three-dimensional, combining current instabilities and sheet tearing on the kinetic level of particle dynamics. The three-dimensional unstable sheet decay is demonstrated by means of simulation runs carried out with our newly developed 3D electromagnetic, fully kinetic particle-in-cell code GISMO.

We have observed non-quasilinear diffusion in the regime t_ac/t_d[1, where t_ac is the autocorrelation time and t_d the diffusion time, in contradiction to accepted theory. The diffusion enhancement was observed in the regime t_g/t_rb]1, where t_g is the linear growth time and t_rb the the resonance broadening time, in agreement with the theoretical prediction of Laval and Pesme (1980, 1983, 1984). If we define the overlap parameter to be A=(pi/2)^2 (2 d_r/d_v)^2 where d_r is the mode resonance width and d_v the intermode separation, then a high overlap parameter is an approximation to a continuous spectrum. The enhancement is seen in spectra initialized with high overlap parameter (A>200), implying that a continuous spectrum might also produce enhanced transport in the nonlinear regime. A possible mechanism for the enhanced diffusion (spontaneous spectrum discretization) is discussed.

The Earth's Foreshock comprises that region of the solar wind outside---but magnetically connected to---the bow shock. The interaction of the solar wind with the Earth's bow shock provides an electron acceleration mechanism (near the point of tangency of the interplanetary magnetic field with the shock), as well as a natural velocity filter for the accelerated electrons. Together, these two processes can produce electron distributions in the Foreshock that are unstable to the generation of Langmuir waves. While there already exist a wealth of satellite measurements of Langmuir waves in the Foreshock, the unstable electron distributions responsible for these waves have, paradoxically, been observed far less frequently. In order to better understand the mutual (nonlinear) interaction of the electron distribution with the waves (including the influence of wave-wave interactions), we have undertaken a series of 1-D Kinetic Vlasov Equation simulations for relevant Foreshock parameters. These simulations demonstrate the subtle interplay between the various nonlinear processes, and shed light on the origin of an anti-beamward plateau observed in some measured distributions.