Bulletin of the American Physical Society
APS April Meeting 2010
Volume 55, Number 1
Saturday–Tuesday, February 13–16, 2010; Washington, DC
Session Q10: Plasma Physics |
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Sponsoring Units: DPP Chair: James Drake, University of Maryland Room: Maryland B |
Monday, February 15, 2010 1:30PM - 1:42PM |
Q10.00001: Well Confined High Density Plasmas as Neutron Sources A. Bianchi, B. Coppi The physics of high density plasmas ($n_{0}\simeq5\times10^{14}-10^{15}$ cm$^{-3}$) that can be well confined in high magnetic field, compact machines, and that can be developed into interesting neutron sources is discussed. Ignitor[1], a machine following a line of which Alcator was the prototype, that has been conceived and designed in order to demonstrate ignition of a D-T burning plasma, can produce up to $3\times10^{19}$ n/sec although with too low a duty cycle. Therefore, a non-igniting, differently conceived device with an adequate duty cycle is being analyzed. An important element for this is the development of cables involving the recently discovered MgB$_{2}$ superconducting material for which the He-gas cryogenic system designed for Ignitor can be adopted. The two largest poloidal (vertical) field coils for Ignitor are in fact designed with these kind of cables. We propose extending the adoption of this material for other magnet systems through a hybrid solution, in contrast to the pure copper solution adopted for Ignitor, taking advantage of the higher current densities that MgB$_{2}$ can sustain, and of the structural characteristics of the relevant cables.\\[4pt] [1] B.Coppi, {\it et al.} Paper FT/P3-23 (Publ. I.A.E.A., Vienna 2008) [Preview Abstract] |
Monday, February 15, 2010 1:42PM - 1:54PM |
Q10.00002: The Effect of SF$_{6}$ dilution in an Argon plasma Sudip Koirala, Matt Gordon Plasma etching is widely used in semiconductor industries. There have been extensive studies in the dilution of rare gases; however, limited studies are found in the dilution of electronegative gases. In this work, SF$_{6}$ content is varied from 5{\%} to 60{\%} in an Ar plasma in a deep reactive ion etching system. A Langmuir probe is used to measure electron temperature (T$_{e})$, electron density (n$_{e})$, and electron energy distribution function (eedf). T$_{e}$ decreases monotonically with increasing SF$_{6}$ at first, and then increases for SF$_{6}$ content greater than 20{\%}. This increase is attributed to the loss of low energy electrons in attachment and high energy electrons in excitation and ionization. As the content of SF$_{6 }$is increased above 20{\%}, the dissociation of SF$_{6}$ increases and most of the low energy electrons are lost in attachment and hence the average electron temperature increases. n$_{e}$ decreases by an order of magnitude as the SF$_{6}$ dilution is increased from 5{\%} to 60{\%}. eedf shows that the distribution shifts towards high energy with the increase of SF$_{6}$ content, which is because of the depletion of low energy electrons. [Preview Abstract] |
Monday, February 15, 2010 1:54PM - 2:06PM |
Q10.00003: Recent Discoveries on the Plasma Environment of Mars as seen by the Radar Sounder on MARS EXPRESS Spacecraft Firdevs Duru, Donald A. Gurnett, David D. Morgan Mars Advanced Radar for Subsurface and Ionospheric Sounding (MARSIS), which is a low-frequency radar on Mars Express, is designed to study the subsurface and ionosphere of Mars. Here, we give an overview of the plasma environment of Mars as seen by MARSIS. With MARSIS, it is possible to obtain the electron densities with both remote sounding and local electron plasma oscillations. Remote sounding of the ionosphere revealed several types of echoes, including oblique echoes which arise from upward bulges in the ionosphere in regions where the crustal magnetic field of Mars is strong and nearly vertical. It is observed that the electron density profiles are in agreement with the Chapman photo-equilibrium model. Local density data revealed steep, transient electron density gradients similar to the ionopause commonly observed at Venus. It also showed that, at altitudes above 300 km, the electron density on the dayside is almost constant at a given altitude range and it increases exponentially with increasing altitude at a fixed solar zenith angle range. [Preview Abstract] |
Monday, February 15, 2010 2:06PM - 2:18PM |
Q10.00004: Passive, precise plasma jet experiments on the sky Philipp Kronberg The typical plasma parameter space has been established for the most luminous, collimated jets in the Universe. They are magnetically dominated energy pipes produced by super-massive black holes, with energy flows in excess of $\sim $ 10$^{42}$ erg s$^{-1}$, over supra-galaxy scales. I discuss these jets with examples, and conclude that all current radio telescopes fall short in resolution to provide the important plasma diagnostics in these systems. The solution is within technological reach, if the full imaging resolution of the Enhanced VLA (EVLA) were increased from the current 35 km to a few hundred km. This can be achieved by additional telescopes (\textit{ca}. 6) in the State of New Mexico. The cost of doing this, $\sim $ {\$}200M, is modest when matched against the potential benefits to plasma and fusion science. [Preview Abstract] |
Monday, February 15, 2010 2:18PM - 2:30PM |
Q10.00005: Observational signatures of sub-Larmor scale magnetic fields in astrophysical objects and HEAD lab experiments Mikhail Medvedev An extensive body of studies indicate that small-scale (sub-Larmor-scale) magnetic turbulence are produced at relativistic shocks, in reconnection events and other high-energy density environments. Here we present a general description of radiation produced by relativistic electrons moving in such fields and stress its non-synchrotron spectral characteristics. We illustrate the results with spectral data from gamma-ray burst observations. [Preview Abstract] |
Monday, February 15, 2010 2:30PM - 2:42PM |
Q10.00006: Stimulated Brillouin Scattering from OMEGA gas-filled hohlraums and NIF hohlraums with gold-boron layers Richard Berger, L. Divol, D. Froula, S. Glenzer, J. Kline, P. Michel, D. Callahan, D. Hinkel, R. London, N. Meezan, L. Suter, E. Williams The long laser pulse length required to achieve ignition on the National Ignition Facility (NIF) creates long scalelength, hot, high-Z plasma inside the hohlraum from which stimulated Brillouin scatter (SBS) is predicted to be greater than 10{\%}. We predicted that adding $\sim $40{\%} Boron to a thin layer of the high-Z wall reduces the predicted SBS to less than 1{\%}. In the past few years, a number of experiments at the OMEGA laser facility have tested elements of the physics of SBS in gold-boron and the modeling tools. The damping rates for plasmas with various gold-boron mixtures were duplicated with mixtures of CO$_{2}$ and hydrocarbon gasses. Use of the rad-hydro code HYDRA for bulk plasma parameters and the paraxial-wave-solver pF3d allowed the measured levels of stimulated Brillouin backscatter in the OMEGA experiments to be predicted in advance of the experiments. Although the SBS increases with the average gain as expected, closer examination shows that, for the same gain, plasmas with very weakly damped ion acoustic waves Brillouin scatter light more strongly than plasmas with more strongly damped ion acoustic waves. The pF3d simulations also show that behavior. SBS from NIF hohlraums with gold-boron layers will be presented. [Preview Abstract] |
Monday, February 15, 2010 2:42PM - 2:54PM |
Q10.00007: Numerical Simulations of Pair Production by Ultraintense Lasers Edison Liang, Alexander Henderson, Pablo Yepes, Hui Chen, Scott Wilks Using a combination of particle-in-cell plasma kinetic codes and the CERN GEANT4 code for pair production, we systematically study the pair production by ultraintense lasers irradiating gold targets. We will present results for the pair production yield and spectra as a function of laser and target parameters, and compare simulation results with recent data from Titan and other laser experiments. Using these we will design future experiments to optimize the pair yield and pair density. Potential applications of these results to both laboratory astrophysics and high density positronium physics will be discussed. [Preview Abstract] |
Monday, February 15, 2010 2:54PM - 3:06PM |
Q10.00008: Monte Carlo Mathematical Modeling and Analysis of Optogalvanic Waveforms FOR 1s$_{5}$-2p$_{j}$ (j = 7,8,9) transitions of Neon in a Hollow Cathode Discharge Kayode Ogungbemi, Xianming Han, Prabhakar Misra The laser optogalvanic (OG) waveforms associated with the 1s$_{5}$ -- 2p$_{j }$(j=7,8,9) transitions of neon in a hollow discharge lamp have been investigated as a function of discharge current (2.0 -- 19.0 mA). We have refined a mathematical model in determining the amplitudes, decay constants, and time constants associated with these transitions. Monte Carlo least-squares fitting of these waveforms has helped to specifically determine the decay rate constant (a$_{i})$, exponential rates (b$_{i})$ and time constant ($\tau )$ parameters associated with the evolution of the OG signals. In our investigation of the 1s$_{5}$ -- 2p$_{j }$(j=7,8,9)$_{ }$optogalvanic transitions of neon, we have measured the intensity of each transition (3.65*10$^{-28}$ , 1.43*10$^{-27}$ and 5.82*10$^{-27}$ cm$^{-1}$/mole-cm$^{-2}$, respectively), which in turn has provided insight into the excitation temperature of the plasma (estimated to be 2847$\pm $285 K). The population distribution of the excited neon atoms in the pertinent energy levels has also been estimated using the Heisenberg Uncertainty Principle. [Preview Abstract] |
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