Experimental and Theoretical Study of the Inhomogeneous Electron Kinetics in the dc Column Plasma

Abstract

The radial change of the electron velocity distribution function and of related macroscopic quantities of the electrons are studied theoretically and experimentally in the positive column plasma of a neon dc low pressure glow discharge. The theoretical investigations are based on the solution of electron kinetic equations. The measurements of electron kinetic quantities are performed by using a single probe technique with automated recording. To avoid the strict treatment of the complicated radially varying electron kinetics in the microphysical description of the column plasma, various simplifications of the appropriate inhomogeneous kinetic equation have been adopted in the past. Recently a strict solution approach of this complex kinetic problem could be developed. Using this strict solution approach and experimentally determined electron kinetic quantities the approximation quality, obtained by applying various simplified approaches to treat the electron kinetics as the conventional homogeneous approach, the nonlocal approach and the local field approximation, is illustrated and critically evaluated in this paper.

Improved Understanding of the Nonlinear Properties of Ionization Instabilities in Plasmas

“…Therefore instead of the Druyvesteyn distribution the solution of the stationary Boltzmann equation in the spatially homogeneous case is used. This so-called "conventional homogeneous approach" [25] yields transport and rate coefficients which are independent of the radial position in the plasma column. Some collision rates strongly depend on E/p 0 .…”

Self-Consistent Description of Radial Space-Charge Confinement in DC Column Plasmas

“…The self-consistent coupling of the spatially resolved treatments of the excited atom kinetics and the electron kinetics is described, in [17,18,21,22].…”

“…However, they did not consistently take into account the coupling of the equations by applying the resulting potential function in an additional treatment of the electron and ion kinetics. Furthermore, the applied treatment of the electrons is based on the so-called nonlocal approach [24] of the radially inhomogeneous kinetic equation and, consequently, represents an additionally simplified description of the space-dependent electron kinetics [18,25].…”

“…In the other approaches [14,16], particle simulation techniques have been used to solve the kinetic equation. However, most of these authors assumed roughly simplified model functions for the radial space-charge potential [4,15,16,19,22,23] or used a potential function resulting from corresponding electrical probe measurements [17,18,21].…”

“…A numerical solution of this equation to describe the electron kinetics in inhert gas dc column plasmas has been performed by several authors [4,[13][14][15][16][17][18][19][20][21][22] recently. Most of these approaches [4,13,15,[17][18][19][20][21][22] are based on the two-term expansion of the electron velocity distribution (EVD) into spherical harmonics. In the other approaches [14,16], particle simulation techniques have been used to solve the kinetic equation.…”