Excitation of IAWs by ions shear flow and electron parallel current in positive-negative ion plasma

Abstract

It is pointed out that the criterion ωpe≪ωp+, ωp− (where ωpj is the plasma oscillation frequency of jth species and j = e, +, −) presented to define pure pair-ion plasma must also be fulfilled to ignore electron dynamics in positive-negative ion plasma. It is also suggested that the potassium (K+) plasma having negative ions of perfluoromethylcyclohexane (C7F14−) produced in Q-machine seems to have a significant number density of electrons; therefore, ion acoustic waves (IAW) may also exist. If T±<Te and ions have field-aligned shear flow, the fluid theory predicts that the IAWs will be excited. The dimensions of experimentally produced plasma are small; therefore, the local theory is applicable only approximately. Since observations show that Te≃T± in the laboratory performed experiments with positive-negative ions, the kinetic theory is also used to look for electron current-driven IAWs. Kinetic theory predicts that IAWs will be highly damped if electrons flow antiparallel to B0 in opposite direction with respect to positive ions. On the other hand, if electrons flow along B0 as is the case of ionospheric plasma, then IAWs become unstable. Thus, field-aligned shear flow of ions and parallel electron current can produce IAWs both in laboratory and astrophysical electron positive negative ion plasmas.