Bulletin of the American Physical Society
67th Annual Gaseous Electronics Conference
Volume 59, Number 16
Sunday–Friday, November 2–7, 2014; Raleigh, North Carolina
Session NR2: Magnetically Enhanced Plasmas |
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Chair: Jon Gudmundsson, University of Iceland Room: State C |
Thursday, November 6, 2014 10:00AM - 10:15AM |
NR2.00001: Effects of anomalous transport on magnetic filter effect Yevgeny Raitses, Igor Kaganovich, Andrei Smolyakov, Winston Frias The application of the magnetic field in a low pressure plasma can cause a spatial separation of cold and hot electron groups. This so-called magnetic filter effect is not well understood and the subject of our studies. In this work, we investigate electron and ion velocity distribution functions in a low pressure plasma discharge with crossed electric and magnetic field. Previous experimental studies showed that the increase of the magnetic field leads to a more uniform profile of the electron temperature across the magnetic field. This surprising result indicates the importance of anomalous electron transport that causes mixing of hot and cold electrons. High-speed imaging revealed a coherent rotating structure with frequency of a few kHz. Theory describing coherent rotating structures and resulting anomalous transport has been developed and points to ionization and electrostatic instabilities as their possible cause [1-3]. The rotating structure affects perturbations of the plasma potential in both azimuthal and axial directions of the plasma discharge. Preliminary results of Particle-in-Cell simulations and Laser-Induced-Fluorescence measurements showed these perturbations alter the ion velocity distribution function. \\[4pt] [1,2] W. Frias, A. I. Smolyakov, I. D. Kaganovich, and Y. Raitses, Phys. Plasmas \textbf{19}, 072112 (2012); Phys. Plasmas~\textbf{2}~, 052108~(2013) \\[0pt] [3] A. I. Smolyakov, W. Frias, I. D. Kaganovich, and Y. Raitses, Phys. Rev. Lett. 111, 115002 (2013). [Preview Abstract] |
Thursday, November 6, 2014 10:15AM - 10:30AM |
NR2.00002: Optical diagnostics of sputtering in magnetically enhanced high-current discharges David Smith, Steven Aceto, Jason Trotter, Timothy Sommerer, James Lawler We have investigated a gallium-based liquid cathode for use in a high-voltage, high-power gas switch for grid-scale electric power conversion. The cathode requirements include conduction of high current density (1-10 A cm$^{\mathrm{-2}})$, preferably at low voltage, along with minimal loss by evaporation and/or sputtering. The approach to satisfy these criteria has been to operate with a modified commercial magnetron system at high pressure where the choice of working comprises the light elements, such as hydrogen or helium. A separate anode is used to form a plane-parallel geometry. We have demonstrated pulsed operation with current densities exceeding 2 A cm$^{\mathrm{-2}}$ and voltages below 200 V, over a pressure range of 50-800 mTorr. The sputtering rate on gallium and other cathode materials has been estimated for various plasma conditions using a line ratio emission spectroscopy diagnostic based on analysis of the radiation trapping. [Preview Abstract] |
Thursday, November 6, 2014 10:30AM - 11:00AM |
NR2.00003: Fluctuations, instabilities and transport in Hall plasma devices Invited Speaker: Andrei Smolyakov Devices with stationary, externally applied, electric field which is perpendicular to a moderate amplitude magnetic field B0, are common in magnetically controlled plasmas. High interest applications involve Penning type plasma sources, magnetrons and magnetic filters, and electric space propulsion such as Hall thrusters. The electric field produces a stationary current due to the E0 $\times$ B0 electron drift, while ions do not feel the magnetic field due to their large Larmor radius. Standard drift modes doe not exist in such plasma but the ExB electron drift in inhomogeneous plasma and inertial (non-magnetized) ion response result in the so called anti-drift mode. The equilibrium electron flow destabilizes this mode and additional destabilization may come from the gradient of the magnetic field. The electron flow also result in instabilities of negative energy ion sound modes destabilized by dissipation due to collisions and sheath impedance. Sheath impedance is a result of fluctuating electric current into the sheath and further taken over by the current in the dielectric wall. Sheath impedance provide boundary conditions for ion sound wave at the boundaries of a finite length plasma. The quantitative characteristics of these instabilities and its potential ramifications for Hall devices are described. [Preview Abstract] |
Thursday, November 6, 2014 11:00AM - 11:30AM |
NR2.00004: Magnatron Deposition Systems Invited Speaker: John Forster |
Thursday, November 6, 2014 11:30AM - 11:45AM |
NR2.00005: Achievement of high atomic hydrogen densities in cylindrical rf plasmas with magnetic field Ursel Fantz, Stefan Briefi Cylindrical rf plasmas in hydrogen with and without an axial magnetic field of up to 120 G are investigated in the pressure range of 0.3 to 10 Pa. The atomic hydrogen density is determined with optical emission spectroscopy, analyzing the Balmer lines and the molecular radiation (Fulcher band). The results obtained by using different coil geometries (4 to 6 turn windings and Nagoya type antenna) as well as different diameters (10 cm and 25 cm) of a quartz, aluminum oxide or aluminum nitride cylinder are compared. RF powers of up to 600 W at a frequency of 13.56 MHz are available for the 10 cm configuration, whereas up to 70 kW power at 1 MHz are used for the 25 cm cylinder. Density ratios of atoms to molecules of up to 0.3 are achieved in both configurations, whereby the achievement in the high power setup is limited by neutral depletion. The influence of the wall material on the atomic densities, and thus the recombination coefficient, will be pointed out. [Preview Abstract] |
Thursday, November 6, 2014 11:45AM - 12:00PM |
NR2.00006: ABSTRACT WITHDRAWN |
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