Recent developments in collisionless reconnection theory: Applications to laboratory and space plasmas
Recent developments in collisionless reconnection theory: Applications to laboratory and space plasmas
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DOI：
10.1063/1.1353803
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发表时间：
2001-04
影响因子：
2.2
通讯作者：
A. Bhattacharjee;Zhiwei Ma;Xiaogang Wang
中科院分区：
文献类型：
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作者：
A. Bhattacharjee;Zhiwei Ma;Xiaogang Wang
非线性无碰撞重联理论和模拟的最新发展有望为实验室和天体物理等离子体物理中的一些突出问题提供解决方案。此类问题的例子包括托卡马克中的锯齿振荡、磁尾亚暴以及脉冲太阳和恒星耀斑。在每个问题中，一个关键问题是识别对破坏场线的机制（电阻率和/或电子惯性）不敏感的快速重联率。 Sweet-Parker 和 Petschek 的经典模型试图在电阻磁流体动力学 (MHD) 领域解决这个问题。然而，上述等离子体是弱碰撞的，因此遵循广义欧姆定律，其中霍尔电流和电子压力梯度项起着至关重要的作用。回顾了最新的关于由广义欧姆定律控制的脉冲（或触发）以及准稳态重联的理论模型和模拟。在脉冲重连问题中，不仅增长率很快，而且增长率的时间导数变化也很快。在稳态重联问题中，重联层的几何特征（即长度和宽度）和重联率得到显式解析表达式。分析结果通过霍尔 MHD 模拟进行测试。虽然重联层的一些几何特征以及重联率对电阻率的弱依赖性让人想起 Petschek 的经典模型，但在霍尔电流和电子压力梯度存在的情况下介导重联动力学的底层波和粒子动力学在本质上是不同的。在理论和观察之间进行定量比较。确定未决和未解决的问题。
Recent developments in the theory and simulation of nonlinear collisionless reconnection hold the promise for providing solutions to some outstanding problems in laboratory and astrophysical plasma physics. Examples of such problems are sawtooth oscillations in tokamaks, magnetotail substorms, and impulsive solar and stellar flares. In each of these problems, a key issue is the identification of fast reconnection rates that are insensitive to the mechanism that breaks field lines (resistivity and/or electron inertia). The classical models of Sweet-Parker and Petschek sought to resolve this issue in the realm of resistive magnetohydrodynamics (MHD). However, the plasmas mentioned above are weakly collisional, and hence obey a generalized Ohm’s law in which the Hall current and electron pressure gradient terms play a crucial role. Recent theoretical models and simulations on impulsive (or triggered) as well as quasi-steady reconnection governed by a generalized Ohm’s law are reviewed. In the impulsive reconnection problem, not only is the growth rate fast but the time-derivative of the growth rate changes rapidly. In the steady-state reconnection problem, explicit analytical expressions are obtained for the geometric characteristics (that is, length and width) of the reconnection layer and the reconnection rate. Analytical results are tested by Hall MHD simulations. While some of the geometric features of the reconnection layer and the weak dependence of the reconnection rate on resistivity are reminiscent of Petschek’s classical model, the underlying wave and particle dynamics mediating the reconnection dynamics in the presence of the Hall current and electron pressure gradient are qualitatively different. Quantitative comparisons are made between theory and observations. Open and unresolved issues are identified.