Bulletin of the American Physical Society
2005 47th Annual Meeting of the Division of Plasma Physics
Monday–Friday, October 24–28, 2005; Denver, Colorado
Session CO1: Basic Plasma: Non-neutral, Strongly Coupled and Other |
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Chair: Bob Bingham, Rutherfor Appleton Laboratory, United Kingdom Room: Adam's Mark Hotel Governor's Square 10 |
Monday, October 24, 2005 2:00PM - 2:12PM |
CO1.00001: Overview of first results from the Columbia Non-neutral Torus T. Sunn Pedersen, J.P. Kremer, R. Lefrancois, Q. Marksteiner, A.H. Boozer, J. Berkery, X. Sarasola, H. Mynick, N. Pomphrey The Columbia Non-neutral Torus (CNT) is now in full operation. CNT is a stellarator dedicated to creating and studying non-neutral plasmas confined on magnetic surfaces, both pure electron and partially neutralized plasmas, and to the creation of the first laboratory electron-positron plasmas. The existence of ultralow aspect ratio nested magnetic surfaces without significant islands or stochastic regions has been confirmed, and the first non-neutral plasmas have been created using thermionic emitters inserted directly into the confined region. The confinement time can be as long as 20 ms, and seems to be limited by transport induced by the presence of the emitter and diagnostic rods that penetrate the electron plasma. Fully 3-D calculations of CNT pure electron equilibria have now been obtained and neoclassical transport calculations including the effects of strong electric fields have been performed. An overview of these and other CNT related results will be presented, along with plans for the second year of operation. [Preview Abstract] |
Monday, October 24, 2005 2:12PM - 2:24PM |
CO1.00002: The Equilibrium of Pure Electron Plasmas Confined on Magnetic Surfaces Remi G. Lefrancois, Thomas Sunn Pedersen, Allen H. Boozer, Jason P. Kremer, Quinn R. Marksteiner The first pure electron plasmas to be confined on magnetic surfaces have recently been produced in the Columbia Non-Neutral Torus (CNT). These low temperature plasmas ($<$15eV) are created by heating biased filaments placed inside the confinement region. A confinement time of approximately 20ms has been achieved, roughly two orders of magnitude longer than predicted for a $\bf{\nabla{B}}$$\times$$\bf{B}$ drift out of the confining volume; an equilibrium has been established. A fully three-dimensional code has been developed to solve the equilibrium equation, and has been applied to the CNT configuration. The numerically calculated density varies significantly on magnetic surfaces for short Debye length plasmas, by as much as a factor of five along the magnetic axis and even more on outer surfaces. These and other numerical predictions will be presented and compared directly to measurements from CNT. This material is based upon work supported by the National Science Foundation under Grant No. 0317359. [Preview Abstract] |
Monday, October 24, 2005 2:24PM - 2:36PM |
CO1.00003: Antihydrogen from merged plasmas - not cold enough to trap? Niels Madsen The merging of antiprotons with a positron plasma is the predominant and most yielding method for cold antihydrogen formation used to date. We present experimental evidence that this method has serious disadvantages for producing antihydrogen cold enough to be trapped. Antihydrogen is neutral but may be trapped in a magnetic field minium. However, the depth of such traps are of order 1~K, shallow compared to the kinetic energies in current antihydrogen experiments. Studying the spatial distribution of the antihydrogen emerging from the ATHENA positron plasma we have, by comparison with a simple model, extracted information about the temperature of the antihydrogen formed. We find that antihydrogen is formed before thermal equilibrium is attained between the antiprotons and the positrons, and thus that further positron cooling may not be sufficient for producing antihydrogen cold enough to be trapped. [Preview Abstract] |
Monday, October 24, 2005 2:36PM - 2:48PM |
CO1.00004: Viscosity of strongly-coupled dusty plasmas in a liquid state J. Goree, Z. Donk\'o, P. Hartmann, K. Kutasi Dusty plasmas, consisting of micron-size polymer spheres that are electrically charged and suspended in a glow-discharge plasma, provide a convenient experimental way to make a strongly-coupled plasma. Experimenters can configure the confinement so that the particles fill a 1D, 2D, or 3D space. Experimenters can observe particle motion directly using video microscopy, and they can manipulate particles using lasers to create, for example, a shear flow. Recent experimental measurements of the viscosity transport coefficient in a 2D monolayer dusty plasma, which we will review, led us to perform 2D non-equilibrium molecular-dynamics simulations with a Yukawa potential. We found that, as with 3D Yukawa and OCP liquid-state strongly-coupled plasmas but unlike most simple liquids, the viscosity has a minimum value at a particular temperature, corresponding to $\Gamma \approx 20$. Our most significant result is that we detected shear thinning, i.e., the viscosity diminishes as the velocity shear increases. This non-Newtonian fluid property was discovered using a method to measure separately the effects of temperature and shear rate on the sheared velocity profile; this method will also be useful in future experiments. [Preview Abstract] |
Monday, October 24, 2005 2:48PM - 3:00PM |
CO1.00005: Phase Transitions in 2-D Dusty Plasmas Christopher Jones, Michael Murillo Dust grains suspended in plasma sheaths typically arrange into a two-dimensional layer. The interactions in the plane have been shown both theoretically and experimentally to be well-characterized by the screened Coulomb, or Yukawa, potential. The macroscopic size of the systems, as well as the fast time scales relative to the comparable colloid systems, allow for convenient comparison with both the simulation and theory of phase transitions in two-dimensional systems. We have performed molecular dynamics simulations of the 2-D Yukawa system, analysis of which leads to bounds on the melting transition in the coupling-screening parameter space. In our studies of melting, we employ the voronoi construction for the analysis of defects and the bond-orientational order parameter for the determination of long-range orientational order. We have also developed a combined radial/angular distribution function, useful for the anisotropic systems near melting. Our goal is to compare simulation results with the competing dislocation-mediated and grain-boundary-mediated theories of 2-D melting in a parameter regime typical of dusty plasmas. [Preview Abstract] |
Monday, October 24, 2005 3:00PM - 3:12PM |
CO1.00006: Void Structure in Complex Plasmas Truell Hyde, Jie Kong, Lorin Matthews, Jerry Reay, Mike Cook, Jimmy Schmoke Dust particles imbedded within a plasma will acquire an electric charge from collisions with free electrons in the plasma. If the ratio of the inter-particle potential energy to the average kinetic energy is sufficient, the particles can form either a ``liquid'' structure with short range ordering or a crystalline structure with longer range ordering. Dust free regions (voids) inside complex plasmas have also been observed to form under microgravity conditions, in sputtering chamber experiments and in a variety of other experimental situations. Experimental observations reveal a stable dust free state often embedded within a dust crystalline structure or liquid state and exhibiting a sharp boundary. A new mechanism for void formation employing an external DC bias on a GEC rf reference cell will be discussed. Experimental results will be shown to be in good agreement with theoretical predictions for this strongly coupled complex plasma system. [Preview Abstract] |
Monday, October 24, 2005 3:12PM - 3:24PM |
CO1.00007: Dynamics in Saturn's F Ring: Orbits of Charged Grains Lorin Matthews, Meihong Sun, Ginger Bryngelson, Truell Hyde The dynamics of Saturn's F Ring have been a matter of curiosity ever since the probes Pioneer 11 and Voyagers 1 and 2 sent back data revealing the ring's unusual features, and are once again of interest as Cassini reached its destination. The F Ring displays clumps, kinks, waves and braids, structures which evolve on the time scale of months. Several models have been proposed to explain these features; most of these invoke perturbations caused by the shepherding moons or km sized moonlets imbedded in the ring and are purely gravitational in nature. These models assume that both the plasma densities at the F Ring and the charges on the grains are small enough that electromagnetic forces can be ignored. This study shows that such electromagnetic forces can lead to significant perturbations of the orbits of micron sized grains, even for very small grain charges, and are also of importance in explaining the observed structure of the F Ring. [Preview Abstract] |
Monday, October 24, 2005 3:24PM - 3:36PM |
CO1.00008: Propagation and maintenance of plasma in a grounded slot and peripheral chamber connected to a capacitive discharge Allan Lichtenberg, Sungjin Kim, Michael Lieberman A capacitive discharge connected through a slot to a peripheral grounded pumping region is a configuration of both theoretical and practical interest. The configuration is used in commercial dual frequency capacitive discharges with one frequency higher than the usual industrial frequency of 13.56 MHz, with application to dielectric etching on large area substrates. In some configurations a dielectric slot surrounding the substrate separates the main plasma from a peripheral pumping region. Ignition of the peripheral plasma produces detrimental effects on processing performance. Discharge models for diffusion and plasma maintenance in the slot have been developed to obtain conditions for ignition of the plasma in the periphery. An experiment has been constructed to compare with and validate theoretical predictions of ignition conditions. Support provided by Lam Research, the state of California MICRO program, NSF Grant ECS-0139956, and UC Discovery Grant from IUCRP. [Preview Abstract] |
Monday, October 24, 2005 3:36PM - 3:48PM |
CO1.00009: Temperature Oscillations in Ultracold Plasmas Michael S. Murillo Although most plasmas exist at temperatures above that needed for ionization, it is now possible to create neutral plasmas with temperatures in the microKelvin range by rapid photoionization of a very cold gas. Because of their very low temperatures, such plasmas have Coulomb coupling parameters (ratio of potential to kinetic energy) as high as $\Gamma\sim 300,000$. Predictions of ultracold plasma behavior [Murillo, PRL {\bf 76}, 115003 (2001)] show that rapid heating occurs as the plasma correlates to form an equilibrium moderately coupled plasma. This prediction has recently been experimentally verified [Chen {\it et al.}, PRL {\bf 93}, 265003 (2004)] and, in addition, strong oscillations in the temperature were observed. I will discuss the basics of ultracold plasmas, the rapid heating mechanism, and give some insight into the temperature oscillations. [Preview Abstract] |
Monday, October 24, 2005 3:48PM - 4:00PM |
CO1.00010: Axial Modeling of an Electric Discharge in Air Harold Ladouceur, Andrew Baronavski, Tzvetelina Petrova An extensive collisional-radiative air-plasma model was developed to study the axial behavior of an electric discharge in a preexisting air plasma column. The model is based upon the numerical solution of the electron Boltzmann equation for the electron energy distribution function coupled with the balance equations of atomic and molecular ions under consideration, and various nitrogen and oxygen species in ground and excited states. The air kinetics model include both physical and chemical processes such as direct excitation and de-excitation, quenching with electrons and heavy particles, ionization, dissociation, attachment, detachment, recombination, charge exchange, and radiation. The local values of the applied electric field between the cathode of a 250 kV Van de Graaf generator and a grounded sphere have been taken from experiment and were used as an input parameter in solving the system of kinetics equations. The local values of the electron energy distribution function, electron density, mean energy, as well as the densities of all species under consideration were obtained as functions of the external imposed electric field. [Preview Abstract] |
Monday, October 24, 2005 4:00PM - 4:12PM |
CO1.00011: Electronic Structure and Equation of State of Warm Dense Gold Vanina Recoules, Patrick Renaudin, Pierre Noiret, Jean Clerouin We present experimental measurements and theoretical estimations of the equation of state and the resistivity of warm dense gold ($\rho$ =0.5 g/cm$^3$). The plasma was obtained in an isochoric plasma closed-vessel (EPI) designed to confine electrical plasma discharge up to 25 kbar. Theoretically, the properties were computed by quantum molecular dynamics simulation in the DFT/LDA approximation. The frequency dependent optical conductivity and the resistivity were evaluated using Kubo-Greenwood formula. The theoretical results reproduce well the experimental data allowing for a detailed interpretation of the theoretical optical conductivities. Drude's law was used to fit this calculated optical conductivities for low frequency to obtained relaxation times and free electrons number. [Preview Abstract] |
Monday, October 24, 2005 4:12PM - 4:24PM |
CO1.00012: Trapping of Intense Electromagnetic Waves in Relativistic Electron Holes Bengt Eliasson, Padma Kant Shukla We consider the nonlinear interactions between intense localized electromagnetic waves (EMWs) and a relativistically hot electron plasma that supports relativistic electron holes (REHs). Such EMW-REH interactions are governed by a coupled nonlinear system of equations composed of the Maxwell equation describing the dynamics of the EMWs and the Poisson-relativistic Vlasov system describing the dynamics of driven REHs. The present nonlinear system of equations admits both linearly trapped discrete number of eigenmodes of the EMWs in a quasi-stationary REH, and a modification of the REH by large-amplitude trapped MWs. The properties of EMS-REH solitary waves are compared with the ones of relativistic solitary waves in cold plasmas. Computer simulations of the relativistic Vlasov and Maxwell-Poisson system of equations show complex interactions between REHs loaded with localized EMWs. [Preview Abstract] |
Monday, October 24, 2005 4:24PM - 4:36PM |
CO1.00013: Self-similar expansion of finite-size non-quasi-neutral plasmas Masakatsu Murakami, Mikhail Basko A new self-similar solution is presented which describes non-relativistic expansion of a finite plasma mass into vacuum. It is the first analytical solution which treats the effect of charge separation in a fully consistent way and allows a self- consistent determination of the position of the ion front and of the maximum energy of accelerated ions. The solution exists only when the ratio $\Lambda =R/\lambda_D$ of the plasma scale length $R$ to the Debye length $\lambda_D$ is invariant, i.e.\ under the condition $T_e(t) \propto \left[n_e(t)\right]^{1-2/\nu}$, where $\nu= 1$, 2, and 3 corresponds, respectively, to the planar, cylindrical, and spherical geometries. For $\Lambda \gg 1$ the position of the ion front and the maximum energy ${\mathcal E}_{i,max}$ of accelerated ions are calculated analytically: in particular, for $\nu=3$ one finds ${\mathcal E}_{i,max} = 2ZT_{e0} W(\Lambda^2/2)$, where $T_{e0}$ is the initial electron temperature, $Z$ is the ion charge, and $W$ is the Lambert W-function. It is argued that, when properly formulated, the results for ${\mathcal E}_{i,max}$ can be applied more generally than the self-similar solution itself. [Preview Abstract] |
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