An introductory guide to fluid models with anisotropic temperatures. Part 1. CGL description and collisionless fluid hierarchy
An introductory guide to fluid models with anisotropic temperatures. Part 1. CGL description and collisionless fluid hierarchy
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DOI：
10.1017/s0022377819000801
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发表时间：
2019-01
影响因子：
2.5
通讯作者：
P. Hunana;P. Hunana;A. Tenerani;G. Zank;E. Khomenko;E. Khomenko;M. Goldstein;G. Webb;P. Cally;M. Collados;M. Collados;M. Velli;L. Adhikari
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作者：
P. Hunana;P. Hunana;A. Tenerani;G. Zank;E. Khomenko;E. Khomenko;M. Goldstein;G. Webb;P. Cally;M. Collados;M. Collados;M. Velli;L. Adhikari
我们提出了一个详细的指南，先进的无碰撞流体模型，将动力学效应纳入流体框架，这是更接近无碰撞动力学描述比传统的磁流体力学。这种流体模型可直接用于模拟大量天体物理等离子体的湍流演化，如日冕和太阳风、星际介质以及吸积盘和星系团。正文可以被看作是朗道流体模型的详细指南，它分为两个部分。第1部分专门介绍通过使用简单（非朗道流体）闭包关闭流体层次结构获得的流体模型。第2部分专门介绍朗道流体密封件。在第1部分中，我们详细讨论了Chew-Goldberger-Low（CGL）的流体模型，以及包含由霍尔项和对压力张量的有限拉莫尔半径修正引入的色散效应的流体模型。我们考虑色散效应引入的非回转热通量矢量。我们研究了平行和倾斜的消防水龙带不稳定性，并表明，非回旋热通量强烈影响这些不稳定性的最大增长率。此外，我们讨论的流体模型，包含的gyrotropic热通量波动的演化方程，并在第四时刻的水平，通过规定一个特定的形式的分布函数关闭。对于双麦克斯韦分布，这样的闭包被称为“正态”闭包。我们还讨论了双κ分布的流体封闭。最后，通过考虑高阶矩的一维Maxwell流体闭包，我们证明了这种流体模型总是不稳定的。因此，最后一个可能的非朗道流体封闭是“正常”封闭，超过四阶矩，朗道流体封闭是必需的。
We present a detailed guide to advanced collisionless fluid models that incorporate kinetic effects into the fluid framework, and that are much closer to the collisionless kinetic description than traditional magnetohydrodynamics. Such fluid models are directly applicable to modelling the turbulent evolution of a vast array of astrophysical plasmas, such as the solar corona and the solar wind, the interstellar medium, as well as accretion disks and galaxy clusters. The text can be viewed as a detailed guide to Landau fluid models and it is divided into two parts. Part 1 is dedicated to fluid models that are obtained by closing the fluid hierarchy with simple (non-Landau fluid) closures. Part 2 is dedicated to Landau fluid closures. Here in Part 1, we discuss the fluid model of Chew–Goldberger–Low (CGL) in great detail, together with fluid models that contain dispersive effects introduced by the Hall term and by the finite Larmor radius corrections to the pressure tensor. We consider dispersive effects introduced by the non-gyrotropic heat flux vectors. We investigate the parallel and oblique firehose instability, and show that the non-gyrotropic heat flux strongly influences the maximum growth rate of these instabilities. Furthermore, we discuss fluid models that contain evolution equations for the gyrotropic heat flux fluctuations and that are closed at the fourth-moment level by prescribing a specific form for the distribution function. For the bi-Maxwellian distribution, such a closure is known as the ‘normal’ closure. We also discuss a fluid closure for the bi-kappa distribution. Finally, by considering one-dimensional Maxwellian fluid closures at higher-order moments, we show that such fluid models are always unstable. The last possible non Landau fluid closure is therefore the ‘normal’ closure, and beyond the fourth-order moment, Landau fluid closures are required.