Instability in a two-ion plasma with mass-related ion drift

The authors investigate the stability of ion acoustic waves in collisionless field-free plasma formed by electrostatically accelerated beams of ions of two different masses streaming through hot electrons. An ion-ion instability occurs when the beam voltage is comparable to the electron temperature. The origin and parameter dependence of this instability are investigated. The effects on marginal stability of beam voltage E, light ion concentration f, and electron-ion temperature ratio theta are indicated in fig. 1. For all values of the ion mass ratio M, the waves are stable at all concentrations if theta is below a minimum value of approximately 3.5