可压缩磁流体动力学湍流中加速粒子的扩散与散射
The diffusion and scattering of accelerating particles in compressible MHD turbulence
AI总结：
本文数值研究压缩MHD湍流中宇宙线的扩散、散射与加速，发现回旋半径指数增长、动量扩散呈幂律或平台，扩散主导模式随阿尔文区变化，加速由快/慢模式主导，磁声模式仍关键。
摘要：
我们在现代磁流体动力学（MHD）湍流理解的框架下，数值研究了宇宙线（CRs）的扩散、散射及其加速过程。基于观测和数值实验获得的压缩MHD湍流特性，我们研究了宇宙线与等离子体模式的相互作用。我们发现：（1）粒子的回旋半径随加速时标呈指数增长；（2）在强湍流区，动量扩散与回旋半径呈幂律关系，而在弱湍流区则呈现平台，暗示存在随机加速过程；（3）在亚阿尔文区，空间扩散以平行扩散为主，而在超阿尔文区则以垂直扩散为主；（4）关于宇宙线与等离子体模式的相互作用，在高$β$情形下粒子加速由快模式主导，而在低$β$情形下由快模式和慢模式共同主导；（5）在存在加速的情况下，磁声模式在宇宙线的扩散和散射过程中仍起关键作用，这与早期的理论预测高度一致。
英文摘要：
We numerically study the diffusion and scattering of cosmic rays (CRs) together with their acceleration processes in the framework of the modern understanding of magnetohydrodynamic (MHD) turbulence. Based on the properties of compressible MHD turbulence obtained from observations and numerical experiments, we investigate the interaction of CRs with plasma modes. We find that (1) the gyroradius of particles exponentially increases with the acceleration timescale; (2) the momentum diffusion presents the power-law relationship with the gyroradius in the strong turbulence regime, and shows a plateau in the weak turbulence regime implying a stochastic acceleration process; (3) the spatial diffusion is dominated by the parallel diffusion in the sub-Alfvénic regime, while it is dominated by the perpendicular diffusion in the super-Alfvénic one; (4) as for the interaction of CRs with plasma modes, the particle acceleration is dominated by the fast mode in the high $β$ case, while in the low $β$ case, it is dominated by the fast and slow modes; (5) in the presence of acceleration, magnetosonic modes still play a critical role in diffusion and scattering processes of CRs, which is in good agreement with the earlier theoretical predictions.
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