Multistream instabilities in three-species plasmas formed around strong double layers

Abstract

An electron–electron–ion (e-e-i) and an ion–ion–electron (i-i-e) plasma are formed on the sides of a strong double layer. A detailed parametric investigation of the linear dispersion relation of these three-species plasmas is carried out in order to determine the different current-driven instabilities that can form in each of them. Both the electron–electron (e-e) and the ion–electron (i-e) instabilities develop in the e-e-i plasma. The first one dominates over practically its whole domain of existence and presents up to five different types. The second one involves the three plasma species and differs from the classical two-species version: it is resistive for most parametric ranges, with the reactive type occupying only a small parametric region within the high-drift range. Either two i-e instabilities or one i-e and one ion–ion instability can develop simultaneously in the i-i-e plasma, depending on the ratio of the velocities of the two beams involved. For both types of plasmas, different forms of branch mixing between the two unstable modes are identified.