Comparisons of computational methods to represent electron transport in nonequilibrium plasma devices
Pak, Hoyoung
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Permalink
https://hdl.handle.net/2142/23337
Description
Title
Comparisons of computational methods to represent electron transport in nonequilibrium plasma devices
Author(s)
Pak, Hoyoung
Issue Date
1991
Doctoral Committee Chair(s)
Kushner, Mark J.
Department of Study
Electrical and Computer Engineering
Discipline
Electrical and Computer Engineering
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Physics, Fluid and Plasma
Language
eng
Abstract
Low pressure optically triggered pseudosparks, or Back-Lit Thyratrons (BLT), are inherently multidimensional transient devices. The method employed to model electron transport in such devices is therefore problematic. A versatile model for these switches with which to compare different modeling approaches has been developed. In the two-dimensional, time dependent model, fluid equations are solved to obtain the electron and ion densities, and Poisson's equation is solved for the electric potential. These equations can be solved using the local field approximation (LFA), employing conservation equations for the bulk electron energy and momentum, or adding multiple beam components to the electron energy distribution. Combinations of these methods can also be employed. The model has been exercised to determine the parameter space, e.g., gas pressure, voltage, electrode gaps, in which each of these methods can be reliably used. Due to the induction time required to achieve quasi-equilibrium conditions, employing the energy equation and beam components typically slows the response of the switch compared to using the LFA.
A separate model has also been developed to study breakdown in BLTs. In parallel plane geometries, the Paschen curve can be used to predict breakdown voltages as a function of $p\cdot d$ (gas pressure $\times$ electrode separation). When electrodes are not planar, i.e., central holes in electrodes, the breakdown deviates from that given by the Paschen curve. The details of the breakdown conditions for hollow electrode geometries have been investigated, and scaling laws derived.
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