Microinstabilities at Quasi-Perpendicular Shocks in the High Beta ICM

Abstract

At quasi-perpendicular shocks in the high- (~100) intracluster medium (ICM), various microinstabilities occurrs by the temperature anisotropies and/or drift motions of plasma. In the downstream, the Alfvén ion cyclotron instability (AIC) due to the ion temperature anisotropy () is triggered by shock-reflected ions, the whistler instability (WI) is driven by the electron temperature anisotropy () as a consequence of the shock compression of magnetic fields, and the mirror instability is generated due to the ion and/or electron temperature anisotropy. At the shock foot, the modified two stream instability (MTSI) is possibly excited by the cross-field drift between ions and electrons. In the upstream, electron firehose instability (EFI) is driven by the electron temperature anisotropy or the relative drift between incoming and reflected electrons. These microinstabilities play important roles in the particle acceleration in ICM shocks, so understanding of the microinstabilities and the resultant plasma waves is essential. In this study, based on a linear stability analysis, the basic properties of the microinstabilities in ICM shocks and the ion/electron scale fluctuations are described. We then discuss the implication of our work on the electron pre-acceleration in ICM shocks.