The influence of proton thermal properties on electromagnetic ion cyclotron wave activity in solar ejecta

The possibility of exciting electromagnetic ion cyclotron waves in solar ejecta was proposed in earlier work (Farrugia et al., JGR 103, 6543–6550 (1998)). Here we focus on the twofold aspect of the effect of the protons on this instability, specifically, the proton thermal anisotropy, ����=T⊥,p/T∥,p−1, and the non-Maxwellian tail representing bidirectionally streaming energetic protons (BPs), which are often observed in solar ejecta. Parameters expected to represent a number of solar ejecta are chosen and kept fixed. We solve the kinetic dispersion relation for a population of protons, electrons, and alpha particles. While ���� does not affect the phase speed of the waves, increasing |A��| leads to a substantial enhancement of growth rates and a widening of the unstable frequency range. Maximum growth rates increase exponentially with |A��|. The BPs are modeled by a κappa distribution along the field in addition to the bi-Maxwellian describing the rest of the population. A linear relation exists between maximum growth rates and the density ratio of κappa proton to Maxwellian protons (η��). Saturation of the width of the unstable frequency range occurs around ����∼10%