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Title: On electron bunching and stratification of glow discharges

Abstract

Plasma stratification and excitation of ionization waves is one of the fundamental problems in gas discharge physics. Significant progress in this field is associated with the name of Lev Tsendin. He advocated the need for the kinetic approach to this problem contrary to the traditional hydrodynamic approach, introduced the idea of electron bunching in spatially periodic electric fields, and developed a theory of kinetic resonances for analysis of moving striations in rare gases. The present paper shows how Tsendin's ideas have been further developed and applied for understanding the nature of the well-known S-, P-, and R-striations observed in glow discharges of inert gases at low pressures and currents. We review numerical solutions of a Fokker-Planck kinetic equation in spatially periodic electric fields under the effects of elastic and inelastic collisions of electrons with atoms. We illustrate the formation of kinetic resonances at specific field periods for different shapes of injected Electron Distribution Functions (EDF). Computer simulations illustrate how self-organization of the EDFs occurs under nonlocal conditions and how Gaussian-like peaks moving along resonance trajectories are formed in a certain range of discharge conditions. The calculated EDFs agree well with the experimentally measured EDFs for the S, P, and Rmore » striations in noble gases. We discuss how kinetic resonances affect dispersion characteristics of moving striations and mention some non-linear effects associated with glow discharge stratification. We propose further studies of stratification phenomena combining physical kinetics and non-linear physics.« less

Authors:
 [1];  [2];  [3]
  1. St. Petersburg State University, St. Petersburg 198504 (Russian Federation)
  2. CFD Research Corporation, Huntsville, Alabama 35805 (United States)
  3. Ukhta State Technical University, Ukhta 169300 (Russian Federation)
Publication Date:
OSTI Identifier:
22218480
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physics of Plasmas; Journal Volume: 20; Journal Issue: 10; Other Information: (c) 2013 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; COMPUTERIZED SIMULATION; DISTRIBUTION FUNCTIONS; ELECTRIC FIELDS; ELECTRONS; FOKKER-PLANCK EQUATION; GAUSS FUNCTION; GLOW DISCHARGES; KINETIC EQUATIONS; NONLINEAR PROBLEMS; NUMERICAL SOLUTION; PERIODICITY; PLASMA; PLASMA SIMULATION; PLASMA WAVES; RARE GASES; STRATIFICATION; STRIATIONS

Citation Formats

Golubovskii, Yuri B., Kolobov, Vladimir I., and Nekuchaev, Vladimir O. On electron bunching and stratification of glow discharges. United States: N. p., 2013. Web. doi:10.1063/1.4822921.
Golubovskii, Yuri B., Kolobov, Vladimir I., & Nekuchaev, Vladimir O. On electron bunching and stratification of glow discharges. United States. doi:10.1063/1.4822921.
Golubovskii, Yuri B., Kolobov, Vladimir I., and Nekuchaev, Vladimir O. Tue . "On electron bunching and stratification of glow discharges". United States. doi:10.1063/1.4822921.
@article{osti_22218480,
title = {On electron bunching and stratification of glow discharges},
author = {Golubovskii, Yuri B. and Kolobov, Vladimir I. and Nekuchaev, Vladimir O.},
abstractNote = {Plasma stratification and excitation of ionization waves is one of the fundamental problems in gas discharge physics. Significant progress in this field is associated with the name of Lev Tsendin. He advocated the need for the kinetic approach to this problem contrary to the traditional hydrodynamic approach, introduced the idea of electron bunching in spatially periodic electric fields, and developed a theory of kinetic resonances for analysis of moving striations in rare gases. The present paper shows how Tsendin's ideas have been further developed and applied for understanding the nature of the well-known S-, P-, and R-striations observed in glow discharges of inert gases at low pressures and currents. We review numerical solutions of a Fokker-Planck kinetic equation in spatially periodic electric fields under the effects of elastic and inelastic collisions of electrons with atoms. We illustrate the formation of kinetic resonances at specific field periods for different shapes of injected Electron Distribution Functions (EDF). Computer simulations illustrate how self-organization of the EDFs occurs under nonlocal conditions and how Gaussian-like peaks moving along resonance trajectories are formed in a certain range of discharge conditions. The calculated EDFs agree well with the experimentally measured EDFs for the S, P, and R striations in noble gases. We discuss how kinetic resonances affect dispersion characteristics of moving striations and mention some non-linear effects associated with glow discharge stratification. We propose further studies of stratification phenomena combining physical kinetics and non-linear physics.},
doi = {10.1063/1.4822921},
journal = {Physics of Plasmas},
number = 10,
volume = 20,
place = {United States},
year = {Tue Oct 15 00:00:00 EDT 2013},
month = {Tue Oct 15 00:00:00 EDT 2013}
}
  • Particle-in-cell Monte Carlo simulations of rf glow discharges between parallel-plate electrodes reveal the possibility of negative period-averaged power deposited into electrons in the body of the glow. A two-fluid model of fast- and slow-electron transport demonstrates that fast electrons are compressed at the plasma-sheath boundary by the expanding sheath and are rarefied at the other (collapsing) sheath, resulting in a fast-electron density gradient through the plasma. The resulting electron acoustic waves are the key to understanding electron cooling in the body of the glow.
  • Glow discharge conditioning of tokamaks with graphite plasma-facing surfaces has been used to reduce impurities and obtain density control of the plasma discharge. However, a major operational disadvantage of glow conditioning is the high pressure required to initiate the glow discharge, e.g., {approx}70 mTorr for helium in DIII-D, which requires isolating auxiliary components that can not tolerate the high pressure. An electron-gun-assisted glow discharge can lower breakdown pressure, possibly eliminating the necessity of isolating these auxiliary systems during glow discharge conditioning and allowing glow discharge operation at lower pressures. An electron-assisted glow discharge experiment has been carried out in amore » small vacuum vessel to evaluate whether such a system can be employed in the DIII-D tokamak. With an electron gun to produce an initial source of electrons, the pressure at which a helium glow discharge can be initiated has been decreased by two orders of magnitude. The glow was produced in a 0.40 m{sup 3} Inconel test chamber (3.5 m{sup 2} surface area) and was pumped with a 330 l/s turbomolecular pump. The electron gun consists of a tungsten filament and grid assembly. An electron current of up to 18 mA with energies up to 1.6 kV has been used. The pressure is measured with a capacitance manometer, the gas composition with a residual gas analyzer and the electron temperature, density, and plasma floating potential with a Langmuir probe. With the addition of an electron current of 10 mA, the initiation pressure was reduced from 165 to 1.6 mTorr. The lowest sustaining pressure dropped from 3.0 mTorr in the absence of electron assist to 1.5 mTorr with 10 mA of electron current.« less
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