Electron cyclotron waves (whistlers), are commonly observed in plasmas near Earth and the solar wind. In the presence of nonlinear mirror modes, bursts of whistlers, usually called lion roars, have been observed within low magnetic field regions associated to these modes. In the intracluster medium (ICM) of galaxy clusters, the excitation of the mirror instability is expected, but it is not yet clear whether electron and ion cyclotron waves can also be present under conditions where gas pressure dominates over magnetic pressure (high $β$). In this work, we perform fully kinetic particle-in-cell (PIC) simulations of a plasma subject to a continuous amplification of the mean magnetic field $\textbf{B}(t)$ to study the nonlinear stages of the mirror instability and the ensuing excitation of whistler and ion cyclotron (IC) waves under ICM conditions. Once mirror modes reach nonlinear amplitudes, both whistler and IC waves start to emerge simultaneously, with sub-dominant amplitudes, propagating in low-$\textbf{B}$ regions, and quasi-parallel to $\textbf{B}(t)$. We show that the underlying source of excitation is the pressure anisotropy of electrons and ions trapped in mirror modes with loss-cone type distributions. We also observe that IC waves play an essential role in regulating the ion pressure anisotropy at nonlinear stages. We argue that whistler and IC waves are a concomitant feature at late stages of the mirror instability even at high-$β$, and therefore expected to be present in astrophysical environments like the ICM. We discuss the implications of our results for collisionless heating and dissipation of turbulence in the ICM.
Whistler-Alfvén turbulence in a non-neutral ultrarelativistic pair plasma
University of Wisconsin at Madison（威斯康星大学麦迪逊分校）；Space Science Institute（空间科学研究所）；University of Kansas（堪萨斯大学）；Massachusetts Institute of Technology（麻省理工学院）
Electron Heating by the Ion Cyclotron Instability in Collisionless Accretion Flows. I. Compression-Driven Instabilities and the Electron Heating Mechanism
Compression-Driven Kinetic Instabilities in Magnetically Arrested Disks
University of Illinois（伊利诺伊大学）；Illinois Center for Advanced Study of the Universe（伊利诺伊大学宇宙高级研究中心）；Columbia University（哥伦比亚大学）；Center for Computational Astrophysics, Flatiron Institute（平顿研究所计算天体物理中心）；Princeton University（普林斯顿大学）；University of Wisconsin–Madison（威斯康星大学麦迪逊分校）
