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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.

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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.

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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) 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.

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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.

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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.

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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)

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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 MHD simulations will also be discussed.

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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.

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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 a 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.

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