Computer study of many waves in the small cold beam and plasma interaction

Abstract

When a small and fast, monoenergetic electron beam enters a relatively cold plasma, the combined system is unstable to the growth of waves. The single wave model does not predict correctly the developed nonlinear wave behaviour observed in experiments. A very broad spectrum of waves is measured, suggesting that many waves determine the later stages of nonlinear development. Fifteen waves were modelled and their linear and nonlinear self-consistent evolution with the beam and a non-resonant plasma were followed. Since nonlinear theory shows that temporally and spatially growing waves satisfy different dispersion relations, the problem was solved for both kinds of boundary conditions. A simple model for nonlinear instability is presented.