Energetic Particle Acceleration in Compressible Magnetohydrodynamic Turbulence
Energetic Particle Acceleration in Compressible Magnetohydrodynamic Turbulence
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DOI：
10.3847/1538-4357/ac28ff
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发表时间：
2021-09
期刊：
影响因子：
--
通讯作者：
Jianfu Zhang;F. Xiang
中科院分区：
文献类型：
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作者：
Jianfu Zhang;F. Xiang
磁流体动力学（MHD）湍流是高能粒子加速的重要因素。针对磁湍流的可压缩特性，采用测试粒子方法研究了实际天体物理环境中可能出现的四种湍流区中粒子的Alfvén、慢、快三种模式的加速.研究表明：（1）无论激波是否出现，二阶Fermi机制都通过粒子与湍流的相互作用驱动着三种模式级联过程中粒子的加速，（2）最大加速率的功率谱不仅可以揭示可压缩湍流的惯性范围，而且可以恢复模式之间的标度关系和能量比关系;（3）在超Alfvénic和超声速湍流中，快模式对粒子加速起主导作用，在亚Alfvénic湍流中，慢模式对粒子加速起主导作用，Alfvén模式对粒子加速的影响在加速的早期阶段非常显著;（4）在一定的演化时间范围内，三种模式下的粒子加速均呈幂律分布。本文从粒子波模相互作用的角度出发，促进了对湍流性质和粒子加速行为的理解，有助于深入了解MHD湍流中涉及的天体物理过程。
Magnetohydrodynamic (MHD) turbulence is an important agent of energetic particle acceleration. Focusing on the compressible properties of magnetic turbulence, we adopt the test particle method to study the particle acceleration from Alfvén, slow, and fast modes in four turbulence regimes that may appear in a realistic astrophysical environment. Our studies show that (1) the second-order Fermi mechanism drives the acceleration of particles in the cascade processes of three modes by particle-turbulence interactions, regardless of whether the shock wave appears; (2) not only can the power spectra of maximum-acceleration rates reveal the inertial range of compressible turbulence, but also recover the scaling and energy ratio relationship between the modes; (3) fast mode dominates the acceleration of particles, especially in the case of super-Alfvénic and supersonic turbulence, slow mode dominates the acceleration for sub-Alfvénic turbulence in the very-high-energy range, and the acceleration of Alfvén mode is significant at the early stage of the acceleration; (4) particle acceleration from three modes results in a power-law distribution in the certain range of evolution time. From the perspective of particle-wave mode interaction, this paper promotes the understanding for both the properties of turbulence and the behavior of particle acceleration, which will help provide insight into astrophysical processes involved in MHD turbulence.