Electromagnetic ion cyclotron instability stimulated by the suprathermal ions in space plasmas: A quasi-linear approach

TL;DR

This study uses a refined quasi-linear approach to show that suprathermal protons significantly enhance the electromagnetic ion cyclotron instability in space plasmas, affecting growth rates, wave-number ranges, and relaxation times.

Contribution

It introduces an improved quasi-linear model that accurately captures the effects of suprathermal ions on EMIC instability evolution in space plasmas.

Findings

Suprathermal protons increase the growth rates of EMIC instability.

Enhanced wave-number range and magnetic energy density at saturation.

Faster relaxation of temperature anisotropy towards isotropy.

Abstract

In collision-poor space plasmas protons with an excess of kinetic energy or temperature in direction perpendicular to background magnetic field can excite the electromagnetic ion cyclotron (EMIC) instability. This instability is expected to be highly sensitive to suprathermal protons, which enhance the high-energy tails of the observed velocity distributions and are well reproduced by the (bi-)Kappa distribution functions. In this paper we present the results of a refined quasilinear (QL) approach, able to describe the effects of suprathermal protons on the extended temporal evolution of EMIC instability. It is thus shown that suprathermals have a systematic stimulating effect on the EMIC instability, enhancing not only the growth rates and the range of unstable wave-numbers, but also the magnetic fluctuating energy density reached at the saturation. In effect, the relaxation of anisotropic temperature becomes also more efficient, i.e., faster in time and closer to isotropy.