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The delta-f algorithm has been implemented in the 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

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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.

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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_θ = 0, k_z = 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.

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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.

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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.

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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 producted 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.

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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.

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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.

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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.

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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.

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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.

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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.

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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.

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