Impact of nonisotropic elastic and inelastic scattering on the electron velocity distribution in weakly ionized plasmas

Abstract

By using appropriate angular distributions for elastic and inelastic scattering of electrons with gas atoms, the effect of nonisotropic elastic and/or inelastic collision processes on electron velocity distribution and corresponding macroscopic quantities, and also on their variations when increasing the approximation orders, is studied for a convenient model plasma. The study is made possible by the use of a new technique for the solution of the Boltzmann equation at elevated orders of approximation based on an appropriate Legendre polynomial expansion of the velocity distribution function. It is found that large variations of the distribution function and relevant macroscopic quantities occur when passing from isotropic scattering to narrow angular distributions of forward scattering in elastic collisions or in both kinds of collision processes. The simultaneous action of the two anisotropies leads to a pronounced amplification of the effect while backward scattering produces less important changes. The effects remarkably increase when decreasing the energy loss per inelastic collision. A microphysical interpretation of the impact of nonisotropic scattering is given in terms of the competing actions of field acceleration and collisional dissipation, which is modified by nonisotropic scattering, and of the reflections on the structure of the hierarchy of equations describing the electron behaviour.