Parametric instabilities generated by an energetic electron beam

Abstract

The large amplitude electron plasma oscillations produced by a low density energetic electron beam can parametrically decay into growing non-resonant electron and ion waves. A similar parametric instability occurs in a plasma driven by a sufficiently strong applied electric field whose frequency is near the electron plasma frequency. A two-specie one-dimensional particle simulation model was used to study the beam-generated parametric instability and the results are compared with corresponding one-specie beam and external field simulations. For low beam densities the individual non-resonant modes grow approximately at the rate predicted by parametric instability theory. The growth of these modes eventually causes the resonant mode energy to decay from its saturation value at a rate proportional to the original parametric growth rate. The electron distribution function fe(v) develops suprathermal tails which cause enhanced non-thermal electric field energy fluctuations whose spectrum W(k<or=0.1ke) approximately k-2.