标题： 阿尔文湍流数值模拟中测试粒子的加热 显示英文标题

标题： 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力学（MHD）湍流（“阿尔芬湍流”）的三维数值模拟中带电测试粒子的加热现象；这些结果与太阳风、太阳耀斑、黑洞吸积盘以及其他天体物理和日球层环境中的粒子加热和加速问题相关。 粒子加热的物理机制取决于粒子的回旋频率是否与计算域中解析出的湍动波动频率相当。 具有近似相等频率的粒子会经历强烈的垂直加热（相对于局部磁场）以及速度角散射。 相比之下，具有大回旋频率的粒子则经历强烈的平行加热。 具有有限电阻率的模拟会在小尺度电流片中产生额外的平行加热，这是由于平行电场的作用。 我们的许多结果与由阿尔芬波和慢模磁声波组成的阿尔芬湍流所引起的粒子加热的线性理论预测一致。 然而，与线性理论预测不同的是，能量交换并非主要由粒子与波之间的离散共振主导；相反，共振效应显著“展宽”。 我们讨论了这些结果对太阳和天体物理学问题的意义，特别是近地太阳风的热力学特性。 我们得出结论，阿尔芬湍流通过粒子与磁场压缩（“慢波”）之间的相互作用产生了显著的平行加热。 然而，在质子朗缪半径以上的尺度上，阿尔芬湍流不会对质子或轻离子产生显著的垂直加热。 显示英文摘要

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.