Alfvenic Turbulence数值模拟中试验粒子的加热
The Heating of Test Particles in Numerical Simulations of Alfvenic Turbulence
摘要：
我们研究了弱可压缩磁流体动力学（MHD）湍流（"Alfvenic湍流“）的三维数值模拟中带电测试粒子的加热;这些结果与太阳风、太阳耀斑、黑洞上的吸积盘以及其他天体物理学和日光层环境中的粒子加热和加速有关。粒子加热的物理学取决于粒子的回转频率是否与在计算域上解析的湍流波动的频率相当。具有这些频率几乎相等的粒子经历强垂直加热（相对于局部磁场）和俯仰角散射。相比之下，具有大回转频率的粒子经历强烈的平行加热。由于小尺度电流片中的平行电场，具有有限电阻率的模拟产生额外的平行加热。我们的许多结果是一致的线性理论预测粒子加热所产生的阿尔文和慢磁声波，使阿尔文湍流。然而，与线性理论的预测相反，能量交换不是由粒子和波之间的离散共振主导的;相反，共振被大大地“加宽”了。我们讨论了我们的结果对太阳和天体物理学问题的影响，特别是近地太阳风的热力学。我们的结论是阿尔文湍流产生显着的平行加热通过粒子和磁场压缩（"慢波“）之间的相互作用。然而，在质子拉莫尔半径以上的尺度上，阿尔文湍流不会产生显著的质子或次要离子的垂直加热。
英文摘要：
We study the heating of charged test particles in three-dimensional numerical simulations of weakly compressible magnetohydrodynamic (MHD) turbulence (``Alfvenic turbulence''); these results are relevant to particle heating and acceleration in the solar wind, solar flares, accretion disks onto black holes, and other astrophysics and heliospheric environments. The physics of particle heating depends on whether the gyrofrequency of a particle is comparable to the frequency of a turbulent fluctuation that is resolved on the computational domain. Particles with these frequencies nearly equal undergo strong perpendicular heating (relative to the local magnetic field) and pitch angle scattering. By contrast, particles with large gyrofrequency undergo strong parallel heating. Simulations with a finite resistivity produce additional parallel heating due to parallel electric fields in small-scale current sheets. Many of our results are consistent with linear theory predictions for the particle heating produced by the Alfven and slow magnetosonic waves that make up Alfvenic turbulence. However, in contrast to linear theory predictions, energy exchange is not dominated by discrete resonances between particles and waves; instead, the resonances are substantially ``broadened.'' We discuss the implications of our results for solar and astrophysics problems, in particular the thermodynamics of the near-Earth solar wind. We conclude that Alfvenic turbulence produces significant parallel heating via the interaction between particles and magnetic field compressions (``slow waves''). However, on scales above the proton Larmor radius, Alfvenic turbulence does not produce significant perpendicular heating of protons or minor ions.
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