Structured Turbulence Collisionless Dynamics and Magnetic Field Generation in Astrophysical Plasmas

摘要-J.C. McWilliams和S.考利 各向异性天体物理等离子体中的结构湍流、无碰撞动力学和磁场产生 本研究计划是对与天体物理发电机特别有关的等离子体湍流的一些基本问题进行研究。 这项研究将使用银河发电机作为主要的天体物理学例子，但其结果也将与原银河发电机和吸积盘发电机有关。 特别是，将研究大普朗特数等离子体中非常小尺度的磁放大的早期阶段和通过逆级联在大尺度上建立磁能的后期阶段，目标如下： (1)通过双极扩散、各向异性粘性或自洽非线性动力学，确定流体湍流粘性耗散范围内尺度上磁能尺度增长的机制。 (2)探索等离子体的物理尺度短的碰撞平均自由程相比，但当演化是慢的碰撞频率相比，并推导出流体方程描述这种物理。 (3)研究具有小尺度强迫的旋转圆盘中的逆叶栅，使得各向异性环境提供螺旋度产生的物理机制。 这些问题在过去没有得到彻底的研究，但它们解决了在实际物理发电机中必须发生的关键过程。分析理论，湍流闭合模型计算，高雷诺数流体方程的直接数值解将被用来攻击这些问题。 动力学方程的渐近分析将被用来描述低碰撞行为。耗散范围磁流体动力学（MHD）将探讨封闭计算和直接数值解在高普朗特数，包括非MHD效应，如部分电离和低碰撞。 也将计算各向异性环境中湍流MHD的直接数值解，在可能的情况下利用渐近约简来降低计算复杂性并增加可分辨尺度的范围，同时保留自洽发电机作用所需的成分。 这项理论研究将解决经常被忽视的问题，小型和大型发电机，并提供高普朗特数和各向异性等离子体湍流的基本理解。 ***

ABSTRACT - J. C. McWilliams and S. Cowley Structured Turbulence, Collisionless Dynamics, and Magnetic Field Generation in Anisotropic Astrophysical Plasmas This research project is an investigation of some basic problems of plasma turbulence which are particularly relevant to astrophysical dynamos. The study will use the galactic dynamo as the primary astrophysical example, but the results will be relevant also to protogalactic and accretion-disk dynamos. In particular, the early stages of magnetic amplification at very small scales in large-Prandtl-number plasmas and the late stages of magnetic energy buildup at large scale by inverse cascade will be studied with the following objectives: (1) To determine mechanisms for magnetic energy scale growth at scales within the viscous dissipation range of fluid turbulence, by ambipolar diffusion, anisotropic viscosity, or self-consistent nonlinear dynamics. (2) To explore the physics of plasmas on scales short compared to the collisional mean free path, but when the evolution is slow compared to the collision frequency, and to derive fluid-like equations that describe this physics. (3) To study the inverse cascade in a rotating disk with small-scale forcing, such that the anisotropic environment provides a physical mechanism for helicity generation. These problems have not been thoroughly studied in the past, yet they address key processes which must occur in actual physical dynamos. Analytical theory, turbulent closure model calculations, and direct numerical solutions of high Reynolds number fluid equations will be used to attack these problems. Asymptotic analysis of kinetic equations will be used to describe low collisionality behavior. Dissipation-range magnetohydrodynamics (MHD) will be explored by closure calculations and direct numerical solutions at high Prandtl number, including non-MHD effects such as partial ionization and low collisionality. Direct numerical solutions of turbulent MHD in an anisotropic environment w ill be also be calculated, making use where possible of asymptotic reductions to decrease computational complexity and increase the range of resolvable scales while retaining the ingredients necessary for self-consistent dynamo action. This theoretical study will address often overlooked questions of small- and large-scale dynamos and provide basic understanding of high Prandtl-number and anisotropic plasma turbulence. ***