Low-Frequency Spatial Response of a Collisional Electron Plasma

Abstract

A study is made of the linear spatial response of an electron plasma to a localized one-dimensional electric field, whose frequency ω is low compared with the electron-collision frequency ν. For a fully ionized plasma, both electron-electron and electron-ion collisions are included in the calculations, the ions being treated as fixed scatterers. It is shown that the neglect of ion dynamics is justified for a suitable choice of parameters. In the hydrodynamic regime, the response function decays exponentially, with decay length equal to a diffusion length a(ων)−½, where a is electron thermal speed, and its amplitude is proportional to ω3/2. In the kinetic regime, the amplitude is proportional to ω, and the decay is not exponential, with characteristic distance being the mean free path a/ν. For a weakly ionized gas, only electron-neutral collisions are included; in the hydrodynamic region, the dependence of amplitude and decay length on ω is the same as for the fully ionized gas, but the decay is no longer exponential.