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

Abstract

In collision-poor space plasmas, protons with an excess of kinetic energy or temperature in the direction perpendicular to the 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 quasi-linear 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 wavenumbers but also the magnetic fluctuating energy density reached at the saturation. In effect, the relaxation of anisotropic temperature also becomes more efficient, i.e., faster in time and closer to isotropy.