An experimental and theoretical investigation of the dynamics of a flowing afterglow plasma

Abstract

A study of plasma and neutral gas flow dynamics has been carried out in pure helium flowing afterglow. The measured plasma flow velocity nu p is observed in effect to be radially independent, in contrast to the instantaneous neutral gas flow velocity profile nu g(r) which is approximately parabolic with some slip at the walls. This observation has led to a new and simplified approach to the flow dynamics based on the concept of a radially independent plasma flow velocity from which, in conjunction with the instantaneous charged particle velocity radial profile (assumed to be equal to nu g(r) and a fundamental mode Bessel radial distribution of charged particle (plasma) density, an averaged plasma flow velocity nu p has been calculated which is shown to be accurately equal to nu p in the approximate pressure range 0.3-0.9 Torr. nu p (hence nu p) is shown to be related to the mean neutral gas flow velocity nu 0 according to nu p approximately 4/3 nu 0.