Two-fluid and kinetic transport physics of Kelvin–Helmholtz instabilities in nonuniform low-beta plasmas
Two-fluid and kinetic transport physics of Kelvin–Helmholtz instabilities in nonuniform low-beta plasmas
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非均匀低β等离子体中开尔文-亥姆霍兹不稳定性的双流体和动力学输运物理学
DOI：
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发表时间：
2020
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通讯作者：
W. Farmer
中科院分区：
文献类型：
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作者：
G. V. Vogman;J. Hammer;U. Shumlak;W. Farmer
利用霍尔磁流体力学（Hall-MHD）理论、双流体模拟和动力学模拟研究了非均匀低β无碰撞等离子体中Kelvin-Helmholtz不稳定性的跨场输运性质。Hall-MHD分析显示了密度梯度和磁化强度如何改变不稳定性的线性特性。高阶精确的双流体和动力学模拟，与完整的动力学有限质量的电子和离子，被施加到一套参数的情况下，系统地评估抗磁漂移，磁化，电荷分离，和有限的拉莫尔运动的影响。精确的两个物种的动力学平衡，有利于孤立的物理效应的研究，并使详细的交叉比较两种流体和动力学模拟，包括离子gyroradii的情况下，梯度尺度长度相媲美。对于具有显著空间电荷的非均匀等离子体，双流体和动力学模拟的结果被发现与Hall-MHD预测不一致。当离子反磁漂移和E × B漂移平行时，单位剪切的Kelvin-Helmholtz不稳定性增长率较小，而当两个漂移反平行时，则较大。这种效应归因于剪切层中的极化漂移，这导致电荷的重新分布，改变驱动等离子体平流的电场，从而修改生长速率。不同参数的不稳定性引起的质量输运的特点是在剪切层和简化的扩散模型的通量。从动力学模拟的分布函数被证明偏离麦克斯韦重建，表明动力学物理的重要性，在非线性阶段的不稳定性。
Hall-magnetohydrodynamic (Hall-MHD) theory, two-fluid simulations, and kinetic simulations are used to investigate the cross-field transport properties of Kelvin–Helmholtz instabilities in nonuniform low-beta collisionless plasmas. Hall-MHD analysis shows how the linear properties of the instability are modified by density gradients and magnetization. High-order accurate two-fluid and kinetic simulations, with complete dynamics of finite-mass electrons and ions, are applied to a suite of parameter cases to systematically assess the effects of diamagnetic drift, magnetization, charge separation, and finite Larmor motion. Initialization of exact two-species kinetic equilibria facilitates the study of isolated physical effects and enables detailed cross-comparisons between two-fluid and kinetic simulations, including for cases where ion gyroradii are comparable to gradient scale lengths. For nonuniform plasmas with significant space charge, the results of two-fluid and kinetic simulations are found to disagree with Hall-MHD predictions. Kelvin–Helmholtz instability growth rates, per unit shear, are shown to be smaller when ion diamagnetic drift and E × B drift are parallel and larger when the two drifts are antiparallel. The effect is attributed to polarization drift in the shear layer, which leads to redistribution of charge, alters the electric field that drives plasma advection, and consequently modifies growth rates. Instability-induced mass transport for different parameters is characterized in terms of the flux across the shear layer and a simplified diffusion model. Distribution functions from kinetic simulations are shown to deviate substantially from Maxwellian reconstructions, indicating the importance of kinetic physics during the nonlinear phase of the instability.