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Title: Nonlocal kinetics of the electrons in a low-pressure afterglow plasma

Abstract

Low-pressure pulsed plasmas are widely used in various technological applications. Understanding of the phenomena taking place in afterglow phase of the discharge makes possible the optimization of the operation conditions and improvement of the technical parameters. At low pressure the electron component of the plasma determines the main features of the discharge since its behavior dominates all other plasma properties. We study the electron kinetics in a low-pressure afterglow plasma of an inductively coupled discharge by means of a self-consistent model which uses the nonlocal kinetic approach. The main features of the model are given. Special attention is paid to determination of the steady state of the discharge from which the decay of the plasma begins. Emphasis is also put on the description of the collisional interaction between the electrons and gas. Results of theoretical investigations for argon at a pressure of 2-4 Pa are presented. Calculated temporal evolutions of the isotropic part of the electron velocity distribution function, electron density, mean electron energy, and wall potential are discussed in comparison with experimental data.

Authors:
; ; ;  [1];  [2]
  1. INP Greifswald, Fr.-L.-Jahn-Strasse 19, Greifswald 17489 (Germany)
  2. (United States)
Publication Date:
OSTI Identifier:
21069775
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physical Review. E, Statistical Physics, Plasmas, Fluids, and Related Interdisciplinary Topics; Journal Volume: 73; Journal Issue: 5; Other Information: DOI: 10.1103/PhysRevE.73.056402; (c) 2006 The American Physical Society; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; AFTERGLOW; ARGON; COMPARATIVE EVALUATIONS; DISTRIBUTION FUNCTIONS; ELECTRIC POTENTIAL; ELECTRON COLLISIONS; ELECTRON DENSITY; ELECTRONS; ION COLLISIONS; KINETICS; OPTIMIZATION; PLASMA; PLASMA DENSITY; STEADY-STATE CONDITIONS

Citation Formats

Gorchakov, Sergey, Uhrlandt, Dirk, Hebert, Michael J., Kortshagen, Uwe, and Department of Mechanical Engineering, University of Minnesota-Twin Cities, 111 Church Street Southeast, Minneapolis, Minnesota 55455. Nonlocal kinetics of the electrons in a low-pressure afterglow plasma. United States: N. p., 2006. Web. doi:10.1103/PHYSREVE.73.056402.
Gorchakov, Sergey, Uhrlandt, Dirk, Hebert, Michael J., Kortshagen, Uwe, & Department of Mechanical Engineering, University of Minnesota-Twin Cities, 111 Church Street Southeast, Minneapolis, Minnesota 55455. Nonlocal kinetics of the electrons in a low-pressure afterglow plasma. United States. doi:10.1103/PHYSREVE.73.056402.
Gorchakov, Sergey, Uhrlandt, Dirk, Hebert, Michael J., Kortshagen, Uwe, and Department of Mechanical Engineering, University of Minnesota-Twin Cities, 111 Church Street Southeast, Minneapolis, Minnesota 55455. Mon . "Nonlocal kinetics of the electrons in a low-pressure afterglow plasma". United States. doi:10.1103/PHYSREVE.73.056402.
@article{osti_21069775,
title = {Nonlocal kinetics of the electrons in a low-pressure afterglow plasma},
author = {Gorchakov, Sergey and Uhrlandt, Dirk and Hebert, Michael J. and Kortshagen, Uwe and Department of Mechanical Engineering, University of Minnesota-Twin Cities, 111 Church Street Southeast, Minneapolis, Minnesota 55455},
abstractNote = {Low-pressure pulsed plasmas are widely used in various technological applications. Understanding of the phenomena taking place in afterglow phase of the discharge makes possible the optimization of the operation conditions and improvement of the technical parameters. At low pressure the electron component of the plasma determines the main features of the discharge since its behavior dominates all other plasma properties. We study the electron kinetics in a low-pressure afterglow plasma of an inductively coupled discharge by means of a self-consistent model which uses the nonlocal kinetic approach. The main features of the model are given. Special attention is paid to determination of the steady state of the discharge from which the decay of the plasma begins. Emphasis is also put on the description of the collisional interaction between the electrons and gas. Results of theoretical investigations for argon at a pressure of 2-4 Pa are presented. Calculated temporal evolutions of the isotropic part of the electron velocity distribution function, electron density, mean electron energy, and wall potential are discussed in comparison with experimental data.},
doi = {10.1103/PHYSREVE.73.056402},
journal = {Physical Review. E, Statistical Physics, Plasmas, Fluids, and Related Interdisciplinary Topics},
number = 5,
volume = 73,
place = {United States},
year = {Mon May 15 00:00:00 EDT 2006},
month = {Mon May 15 00:00:00 EDT 2006}
}
  • Two different kinetic calculations have been employed to investigate the processes governing the formation of the electron distribution function (EDF). One approach involves a numerical {open_quote}{open_quote}propagator{close_quote}{close_quote} treatment of time-resolved electron motion in five-dimensional phase space (two spatial and three velocity coordinates) based on the {open_quote}{open_quote}convected scheme{close_quote}{close_quote} (CS). The other one, referred to as the {open_quote}{open_quote}nonlocal{close_quote}{close_quote} approach, uses the difference between momentum and energy relaxation rates of electrons to simplify the Boltzmann equation. For the majority of electrons, the nonlocal approach reduces the kinetic equation for the isotropic part of the EDF to a form that exhibits a resemblance to thatmore » for homogeneous plasmas. Both calculations incorporate the principal physical effects in a collisional ICP: electron heating by an inductive electric field and nonlocal electron kinetics in which the electrons rapidly lose momentum but travel long distances before suffering a substantial energy loss in collisions. The collision processes that are important in the discharge include quasielastic and inelastic collisions with heavy particles and electron-electron interactions. A comparison of the results of the two methods validates the assumptions employed in the nonlocal approach for the considered range of discharge conditions. To good accuracy the EDF of the majority of the electrons in the ICP is found to be solely a function of the total (kinetic plus potential) electron energy and to be largely independent of the spatial coordinates. The extent to which this is true, and the circumstances under which it is true, are a major focus of this paper. In a rare gas ICP, as a result of Coulomb collisions between electrons, a Maxwell-Boltzmann distribution is typically found in the elastic energy range. (Abstract Truncated)« less
  • Kinetics of positive ions and electrically neutral active particles formed during breakdown and successive discharge in neon-filled tube at 6.6 millibars pressure had been analyzed. This analysis was performed on the basis of mean value of electrical breakdown time delay t{sup ¯}{sub d} dependence on afterglow period τ (memory curve). It was shown that positive ions are present in the 1μs < τ < 30 ms interval, which is manifested through t{sup ¯}{sub d} slow increase with the increase of τ. A rapid t{sup ¯}{sub d} increase in the 30 ms < τ < 3 s interval is a consequence of significant decrease of positive ions concentration and dominant role inmore » breakdown initiation have ground state nitrogen atoms, which further release secondary electrons from the cathode by catalytic recombination process. These atoms are formed during discharge by dissociation of ground state nitrogen molecules that are present as impurities in neon. For τ > 3 s, breakdown is initiated by cosmic rays and natural radioactivity. The increase of discharge current leads to decrease of t{sup ¯}{sub d} due to the increase of positive ions concentration in inter electrode gap. The increase of applied voltage also decreases t{sup ¯}{sub d} for τ > 30 ms due to the increase of the probability for initial electron to initiate breakdown. The presence of UV radiation leads to the decrease of t{sup ¯}{sub d} due to the increased electron yield caused by photoelectrons. The influence of photoelectrons on breakdown initiation can be noticed for τ > 0.1 ms, while they dominantly determine t{sup ¯}{sub d} for τ > 30 ms.« less
  • Effects associated with nonlocality of the electron energy distribution function (EEDF) in a bounded, low-temperature plasma containing fast electrons, can lead to a significant increase in the near-wall potential drop, leading to self-trapping of fast electrons in the plasma volume, even if the density of this group is only a small fraction ({approx}0.001%) of the total electron density. If self-trapping occurs, the fast electrons can substantially increase the rate of stepwise excitation, supply additional heating to slow electrons, and reduce their rate of diffusion cooling. Altering the source terms of these fast electrons will, therefore, alter the near-wall sheath and,more » through modification of the EEDF, a number of plasma parameters. Self-trapping of fast electrons is important in a variety of plasmas, including hollow-cathode discharges and capacitive rf discharges, and is especially pronounced in an afterglow plasma, which is a key phase of any pulse-modulated discharge. In the afterglow, the electron temperature is less than a few tenths of an electron volt, and the fast electrons will have energies typically greater than an electron volt. It is shown that in the afterglow plasma of noble gases, fast electrons, arising from Penning ionization of metastable atoms, can lead to the above condition and significantly change the plasma and sheath properties. Similar effects can be important in technologically relevant electronegative gas plasmas, where fast electrons can arise due to electron detachment in collisions of negative ions with atomic species. Both experimental and modeling results are presented to illustrate these effects.« less