Astrophysical gyrokinetics: Turbulence in pressure-anisotropic plasmas at ion scales and beyond
Astrophysical gyrokinetics: Turbulence in pressure-anisotropic plasmas at ion scales and beyond
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天体物理回旋动力学：离子尺度及以上压力各向异性等离子体中的湍流
DOI：
10.1017/s0022377818000296
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发表时间：
2017
期刊：
影响因子：
--
通讯作者：
A. Schekochihin
中科院分区：
文献类型：
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作者：
M. Kunz;I. Abel;K. Klein;A. Schekochihin
我们提出了一个理论框架来描述电磁动力学湍流在多物种，磁化，压力各向异性等离子体。湍流波动被假定为是小的平均场相比，相对于它是空间各向异性的，并具有频率小的离子回旋频率相比。在离子拉莫尔半径以上的尺度上，该理论简化为Kunz等人（2015）制定的动力学简化磁流体力学（KRMHD）的压力各向异性概括。在离子拉莫尔半径和以下的尺度上，实现了三个主要目标。首先，我们分析的压力各向异性gyrokinetic系统的线性响应，并表明它是一个概括以前探索的限制。压力各向异性的影响的稳定性和碰撞阻尼的Alfvenic和压缩波动的突出，注意的频谱位置和宽度的频率跳跃发生的Alfven波过渡到动力学Alfven波。其次，我们推导并讨论了一个一般的自由能守恒定律，它既捕获了长波长的KRMHD自由能守恒，又捕获了亚离子拉莫尔尺度的动力学阿尔芬波和离子熵的双重级联。我们发现，非麦克斯韦功能的分布函数中的相混合量和磁应力的效率的变化，从而影响级联通道之间的自由能的分区。第三，一个简单的模型被用来表明，压力各向异性可以导致大的变化，由于阿尔芬湍流耗散的离子-电子加热比。我们的理论提供了一个基础，以确定如何压力各向异性影响的湍流波动谱，粒子种类的差分加热，以及空间和天体物理等离子体中的平行和垂直相混合的比例。
We present a theoretical framework for describing electromagnetic kinetic turbulence in a multi-species, magnetized, pressure-anisotropic plasma. Turbulent fluctuations are assumed to be small compared to the mean field, to be spatially anisotropic with respect to it, and to have frequencies small compared to the ion cyclotron frequency. At scales above the ion Larmor radius, the theory reduces to the pressure-anisotropic generalization of kinetic reduced magnetohydrodynamics (KRMHD) formulated by Kunz et al. (2015). At scales at and below the ion Larmor radius, three main objectives are achieved. First, we analyse the linear response of the pressure-anisotropic gyrokinetic system, and show it to be a generalisation of previously explored limits. The effects of pressure anisotropy on the stability and collisionless damping of Alfvenic and compressive fluctuations are highlighted, with attention paid to the spectral location and width of the frequency jump that occurs as Alfven waves transition into kinetic Alfven waves. Secondly, we derive and discuss a general free-energy conservation law, which captures both the KRMHD free-energy conservation at long wavelengths and dual cascades of kinetic Alfven waves and ion entropy at sub-ion-Larmor scales. We show that non-Maxwellian features in the distribution function change the amount of phase mixing and the efficiency of magnetic stresses, and thus influence the partitioning of free energy amongst the cascade channels. Thirdly, a simple model is used to show that pressure anisotropy can cause large variations in the ion-to-electron heating ratio due to the dissipation of Alfvenic turbulence. Our theory provides a foundation for determining how pressure anisotropy affects the turbulent fluctuation spectra, the differential heating of particle species, and the ratio of parallel and perpendicular phase mixing in space and astrophysical plasmas.
DOI：
10.1088/0004-637x/807/1/39
发表时间：
2014-03
期刊：
The Astrophysical Journal
影响因子：
--
作者：
B. Chandran;A. Schekochihin;A. Mallet
通讯作者：
B. Chandran;A. Schekochihin;A. Mallet