Dust in plasmas: Microscopic and macroscopic modeling of particulate-contaminated glow discharges
McCaughey, Michael Joseph, III
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Permalink
https://hdl.handle.net/2142/19211
Description
Title
Dust in plasmas: Microscopic and macroscopic modeling of particulate-contaminated glow discharges
Author(s)
McCaughey, Michael Joseph, III
Issue Date
1991
Doctoral Committee Chair(s)
Kushner, Mark J.
Department of Study
Electrical and Computer Engineering
Discipline
Electrical Engineering
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Engineering, Electronics and Electrical
Physics, Fluid and Plasma
Language
eng
Abstract
Glow discharges are often contaminated by particulates resulting from gas phase nucleation or sputtering of surfaces in contact with the plasma. If these particulates are sufficiently large, they will negatively charge and act as coulomb-like scattering centers for electrons. When this occurs, rate coefficients for high-threshold processes such as ionization may be reduced compared to those in pristine plasmas. If the contamination is nonuniform, then the resulting spatial irregularities in the rates of excitation may lead to plasma properties which are also nonuniform.
Two models have been developed to study the problem of dusty glow discharges: a Monte Carlo microscopic simulation of electron swarms in dusty plasmas, and a multi-dimensional continuum model of a typical glow discharge device. The microscopic model examines the plasma local to a dust particle and generates electron impact rate coefficients for use by the continuum model. The models allow parameterization of discharge system behavior as a function of dust size, density, and spatial distribution.
Results of the models for low-pressure argon and silane discharges indicate that electron impact rate coefficients, particularly for high-threshold processes such as ionization, are strongly reduced by the presence of dust. This effect increases with increasing dust densities; however, this effect is less pronounced in regions where E/N values are high. Under quasi-steady-state conditions, current flow and the subsequent excitation of the gas are channeled into regions of lower dust density, and these effects depend on the density, size and distribution of the dust. In low-pressure ($$ 10$\sp5$cm$\sp{-3}$Torr for 10 cm$\sp{-3}$ $<$ N$\sb{\rm d} <$ 10$\sp9$ cm$\sp{-3}$ and P $<$ 50 Torr.
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