Effects of a slow ion beam on ion-acoustic waves

The influence of a slow ion beam on an ion-acoustic wave was studied. A kinetic dispersion relation of an ion-beam-plasma system, that predicts a critical value of the ion beam density above which the ion-acoustic wave propagates without transforming into the fast mode of space charge waves for any beam velocity, was presented. It was shown that below the critical value, the ion-acoustic wave propagates without transforming into the fast mode of space charge waves for any beam velocity. It was also shown that a dispersion relation based on a fluid model does not provide such a critical value for the ion-beam density.