Free-Streaming and Spatial Landau Damping

Abstract

The interpretation of experiments on the spatial Landau damping of an electrostatic disturbance is shown to be complicated by the contribution of the free-streaming, initially perturbed particles. In particular, unless measurements give the ratio of the imaginary part to the real part of the wave-number to be somewhat less than about 0.4, the observation may be explained using a simple model which neglects the mutual interaction between the plasma particles.