Partially Ionized Gases

The NATO . Advanced Research Insti tute on Nonequilibrium Processes in Partially Ionized Gases was held at Acquafredda di Maratea during 4-17 June 1989. The Institute considered the interconnections between scattering and transport theories and modeling of nonequilibrium systems generated by electrical discharges, emphasizing the importance of microscopic processes in affecting the bulk properties of plasmas. The book tries to reproduce these lines. In particular several contributions describe scattering cross sections involving electrons interacting with atoms and molecules in both ground and excited states (from theoretical and experimental point of view), of energy transfer processes as well as reactive ones involving excited molecules colliding with atoms and molecules as well as with metallic surfaces. Other contributions deal with the basis of transport theories (Boltzmann and Monte Carlo methods) for describing the bulk properties of non equilibrium plasmas as well as with the modeling of complicated systems emphasizing in particular the strong coupling between the Boltzmann equation and excited state kinetics. Finally the book contains several contributions describing applications in different fields such as Excimer Lasers, Negative Ion Production, RF Discharges, Plasma Chemistry, Atmospheric Processes and Physics of Lamps. The Organizing Committee gratefully acknowledges the generous financial support provided by the NATO Science Committee as well as by Azienda Autonoma di Soggiorno e Turismo of Maratea, by University of Bari, by C. N. R. (Centro di Studio per la Chimica dei Plasmi and Comitato per la Chimica), by ENEA, by Lawrence Livermore Laboratory and by US Army Research Office.

When a laser beam of sufficiently high intensity interacts with a weakly ionized gas, the nonuniform deposition of laser energy into the electron gas causes heating of the electrons, ions, and neutral gas. Eventually, the neutral gas will 'break-down' and become more highly ionized. This ionization can seriously limit the amount of laser energy that can damage a target. A multifluid model has been devised to describe the many physical processes that occur when the high power laser wave interacts with the partially ionized gas. A flexible computer program has been developed to numerically integrate the multifluid plasma transport equations coupled with Maxwell's equations. The computer program is sufficiently general so as to be capable of describing target vaporization, with diffusion and ionization of target material into an ambient gas. In this report, only the modification of an ambient gas by the laser radiation is studied.

Transport phenomena in plasmas are the relatively slow processes of particle momentum and energy transport systems in a state of mechanical equilibrium. In contrast to neutral gases, these phenomena in plasmas are greatly influenced by self-consistent fields, in particular electric fields. These can produce particle and energy fluxes, in addition to those generated by the inhomogeneity of the plasma composition and temperature. As a result, the physical effects accompanying transport phenomena in plasmas are far more numerous and complicated than those in neutral gases, and the solution of corresponding problems is more difficult. The effects, however, are usually far more interesting and sometimes surprising. This book presents a systematic survey and analysis of the main mechanisms of transport phenomena in plasma and gives examples of gradually increasing complexity to illustrate these mechanisms and the relationships between them. The author pays special attention to the analysis of experimental measurements and considers the relevant processes analytically as well as qualitatively. The majority of problems dealt with in this book are of considerable practical interest, and the phenomena described often determine the main characteristics of processes and devices. Transport Phenomena in Partially Ionized Plasma will be of interest to researchers who need to know the properties of real, specific systems, as well as to engineers and advanced students in the physics of plasmas, semiconductors, various types of gas discharges and the ionosphere.