Ion acoustic mode in permeating plasmas

Abstract

In the presence of an electron drift relative to ions, the ion acoustic wave is subject to the kinetic instability which takes place if the directed electron speed exceeds the ion acoustic speed. The instability threshold is very different in the case of one quasi-neutral electron-ion plasma propagating through another quasi-neutral (target) plasma. The threshold velocity of the propagating plasma may be well below the ion acoustic speed of the static plasma.