Time evolution of the electron diffusion region and the reconnection rate in fully kinetic and large system
Time evolution of the electron diffusion region and the reconnection rate in fully kinetic and large system
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DOI：
10.1063/1.2220534
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发表时间：
2006-07-01
影响因子：
2.2
通讯作者：
Fujimoto, Keizo
中科院分区：
文献类型：
--
作者：
Fujimoto, Keizo
在大型系统中使用 2-1/2 维全动力学模拟研究嵌入离子级扩散区域的电子扩散区域的时间演化以及与磁重联相关的重联率，因此下游边界条件的任何影响都可以忽略不计。该模拟代码在传统的粒子内单元代码中采用了自适应网格细化技术和粒子分裂算法，这使得我们能够进行大规模的全粒子模拟。结果表明，重联率随着磁重联的增加而增加，并达到足以实现快速重联的峰值，但随后随着时间的推移而下降，尽管系统边界的影响可以忽略不计。减缓重连接过程的关键过程是电子扩散区域的延伸以及电子流入区域中指向中性片的极化电场的增强。极化电场是由离子和电子之间的惯性差引起的，并通过背景离子的曲折运动而增强。为了证实极化电场的作用，我们比较了m(i)/m(e)=1和100的模拟结果。发现(1)在不出现极化电场的系统中实现了准稳态重联，(2)即使在没有霍尔效应的系统中也获得了很大的重联率。这表明可能需要由布尼曼型不稳定性引起的反常电阻率来支持稳态快速重连。 (c) 2006 年美国物理研究所。
Time evolutions of the electron diffusion region embedded in the ion-scale diffusion region and the reconnection rate associated with magnetic reconnection are investigated using 2-1/2 dimensional full kinetic simulations in a large system, so that any effects of the downstream boundary conditions are negligible. The simulation code employs the adaptive mesh refinement technique and the particle splitting algorithm to the conventional particle-in-cell code, which enable us to perform large-scale full particle simulations. It is shown that the reconnection rate increases associated with magnetic reconnection and reaches a peak value large enough for fast reconnection, but then it decreases as time goes on, even though the effects of the system boundary are negligible. The key process responsible for slowing the reconnection processes is the extension of the electron diffusion region in association with the enhancement of the polarization electric field directing toward the neutral sheet in the electron inflow region. The polarization electric field is caused by the inertia difference between ions and electrons, and enhanced by the meandering motions of the background ions. In order to confirm the role of the polarization electric field, we compare the simulation results with m(i)/m(e)=1 and 100. It is found that (1) a quasi-steady reconnection is achieved in the system where the polarization electric field does not arise, (2) a large reconnection rate is obtained, even in the system without the Hall effects. It is suggested that the anomalous resistivity due to the Buneman-type instability might be required to support a steady-state fast reconnection. (c) 2006 American Institute of Physics.