Occurrence of oscillatory modes in a diode with counter-streaming electron and ion flows

Abstract

Plasma devices, as well as some astrophysical objects, are often characterized by the presence of the counterstreaming flows of electrons and positively charged particles in the plasma. In such diodes, more than one stationary solution is possible for the same set of diode parameters. In this paper, we have studied the stability of the most complex solutions, which are characterized by the presence of the potential barriers for both electrons and ions in the plasma gap. It was discovered that there exists a threshold for the value of the electron current, above which the solutions become unstable with respect to small perturbations. In this case, the solutions with nonlinear oscillations appear in the diode instead of stationary solutions. The period of these oscillations is compared to the average time of ion flight across the plasma gap. The features of time-dependent solutions have been studied. In particular, it is found that the electron current passing through the diode in the course of oscillations exceeds that corresponding to the steady states.