Transverse ion heating in multicomponent plasmas along auroral zone field lines

Abstract

In this paper we consider plasma modes that can occur in a multicomponent plasma that includes heavy ions, as well as the effect these modes have on ion acceleration. It is found that, when in the presence of an auroral electron beam, the addition of heavy ions excites an ion‐ion hybrid mode and a modified lower hybrid mode. For a given electron beam, the dominant instability is dependent on Ωe/ωpe and nH/no, and it therefore varies between different regions of the auroral field lines [Schriver and Ashour‐Abdalla, 1988]. In an attempt to gain an understanding of ion heating, we have undertaken a parametric simulation study for changing plasma conditions observed in the auroral zone. The study revealed that for Ωe/ωpe < 10 and no > nH, hydrogen ions were bulk heated, whereas for lower oxygen concentrations, no ≪ nH, hydrogen distribution developed a high‐energy tail. With Ωe ≫ ωpe, a substantial heating of the oxygen distribution was observed; this heating was found to be independent of the oxygen density concentration. This paper also presents a classification system for the different types of heating as functions of altitude along auroral field lines.