弱准垂直激波过渡区的微不稳定性
Microinstabilities in the Transition Region of Weak Quasi-Perpendicular Intracluster Shocks
摘要：
微不稳定性在无碰撞激波的熵产生和粒子加速中起着重要的作用。最近的研究表明，在准垂直的过渡区，（$Q_{\perp}$）高β值的冲击（$β=P_{\rm gas}/P_{\rm B}$）团簇内介质（ICM）中，由于反射回旋离子引起的离子温度各向异性会触发Alfvén离子回旋（AIC）不稳定性和离子镜不稳定性，而由磁场压缩引起的电子温度各向异性会激发哨声不稳定性和电子镜不稳定性。采用粒子模拟中发现的离子和电子温度各向异性的数值估计$Q_{\perp}$ -激波与音速马赫数，$M_{\rm s}=2-3$，我们进行了线性稳定性分析，这些微观不稳定性。的微观不稳定性和随后的等离子体波的离子和电子尺度上的动力学性质进行了描述的参数范围很广，包括依赖于$β$和离子-电子质量比。此外，诱导等离子体波的非线性演化进行检查，通过执行二维PIC模拟与周期性边界条件。我们发现，对于$β\approx 20-100$，AIC不稳定性可以诱导离子尺度波，并在AIC临界马赫数$M_{\rm AIC}^{*} \approx 2.3$以上的超临界激波中产生激波表面波纹。电子尺度波也主要是由这些高$β$激波中的哨声不稳定性产生的。由此产生的多尺度波从电子到离子尺度被认为是必不可少的电子注入到扩散冲击加速机制在$Q_{\perp}$ -冲击在ICM。
英文摘要：
Microinstabilities play important roles in both entropy generation and particle acceleration in collisionless shocks. Recent studies have suggested that in the transition zone of quasi-perpendicular ($Q_{\perp}$) shocks in the high-beta ($β=P_{\rm gas}/P_{\rm B}$) intracluster medium (ICM), the ion temperature anisotropy due to the reflected-gyrating ions could trigger the Alfvén ion cyclotron (AIC) instability and the ion-mirror instability, while the electron temperature anisotropy induced by magnetic field compression could excite the whistler instability and the electron-mirror instability. Adopting the numerical estimates for ion and electron temperature anisotropies found in particle-in-cell (PIC) simulations of $Q_{\perp}$-shocks with sonic Mach numbers, $M_{\rm s}=2-3$, we carry out a linear stability analysis for these microinstabilities. The kinetic properties of the microinstabilities and the ensuing plasma waves on both ion and electron scales are described for wide ranges of parameters, including the dependence on $β$ and the ion-to-electron mass ratio. In addition, the nonlinear evolution of induced plasma waves are examined by performing 2D PIC simulations with periodic boundary conditions. We find that for $β\approx 20-100$, the AIC instability could induce ion-scale waves and generate shock surface ripples in supercritical shocks above the AIC critical Mach number, $M_{\rm AIC}^{*} \approx 2.3$. Also electron-scale waves are generated primarily by the whistler instability in these high-$β$ shocks. The resulting multi-scale waves from electron to ion scales are thought to be essential in electron injection to the diffusive shock acceleration mechanism in $Q_{\perp}$-shocks in the ICM.
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