Resistively-limited current sheet implosions in planar anti-parallel (1D) and null-point containing (2D) magnetic field geometries
Resistively-limited current sheet implosions in planar anti-parallel (1D) and null-point containing (2D) magnetic field geometries
复制标题
平面反平行 (1D) 和包含零点 (2D) 磁场几何形状中的电阻限制电流片内爆
DOI：
10.1063/1.5035489
复制
发表时间：
2018
影响因子：
2.2
通讯作者：
J. A. McLaughlin
中科院分区：
文献类型：
--
作者：
J. Thurgood;D. Pontin;J. A. McLaughlin
电流片的内爆形成是一个基本的等离子体过程。以前的研究主要集中在早期的演变，而在这里，我们的主要目标是探索长期的演变，这可能是决定能量释放效率的关键。为了解决这个问题，我们调查两个密切相关的问题，即：（i）1D，捏反平行磁场和（ii）2D，零点包含场是局部不平衡的（“零崩溃”或“X点崩溃”）。在电阻MHD的框架内，我们模拟了完整的非线性演化通过三个不同的阶段：初始内爆，其最终停止机制，和随后的演变后停止。在一个参数的研究中，我们发现缩放与电阻率的电流片性能在停止时间是在良好的协议-在两个几何形状-从一个已知的一维相似性解决方案推断。我们发现，突然欧姆加热的电流片内的致密等离子体，这提供了一个压力梯度足以反对进一步崩溃和减速的收敛流达到扩散尺度后，迅速停止的内爆发生。这种反压力增长到超过力平衡所需的压力，因此内爆后的演化的特征是电流片向外“反弹”的后果。这些是：（i）发射传播快速MHD波（冲击）向外和（ii）电流片本身的宽度方向的扩展。只有在2D情况下才观察到膨胀失速，在这种情况下，通过重连射流中的流出来缓解压力。在2D的情况下，我们量化的最大量的电流片膨胀，因为它与电阻率的比例，并分析的结构的重连区域，形成后膨胀，充满了Petschek型的慢冲击和快速终止冲击。
Implosive formation of current sheets is a fundamental plasma process. Previous studies focused on the early time evolution, while here our primary aim is to explore the longer-term evolution, which may be critical for determining the efficiency of energy release. To address this problem we investigate two closely-related problems, namely: (i) 1D, pinched anti-parallel magnetic fields and (ii) 2D, null point containing fields which are locally imbalanced ('null-collapse' or 'X-point collapse'). Within the framework of resistive MHD, we simulate the full nonlinear evolution through three distinct phases: the initial implosion, its eventual halting mechanism, and subsequent evolution post-halting. In a parameter study, we find the scaling with resistivity of current sheet properties at the halting time is in good agreement - in both geometries - with that inferred from a known 1D similarity solution. We find that the halting of the implosions occurs rapidly after reaching the diffusion scale by sudden Ohmic heating of the dense plasma within the current sheet, which provides a pressure gradient sufficient to oppose further collapse and decelerate the converging flow. This back-pressure grows to exceed that required for force balance and so the post-implosion evolution is characterised by the consequences of the current sheet `bouncing' outwards. These are: (i) the launching of propagating fast MHD waves (shocks) outwards and (ii) the width-wise expansion of the current sheet itself. The expansion is only observed to stall in the 2D case, where the pressurisation is relieved by outflow in the reconnection jets. In the 2D case, we quantify the maximum amount of current sheet expansion as it scales with resistivity, and analyse the structure of the reconnection region which forms post-expansion, replete with Petschek-type slow shocks and fast termination shocks.
DOI：
10.3847/1538-4357/aabad4
发表时间：
2018-04
期刊：
The Astrophysical Journal
影响因子：
--
作者：
T. Forbes;D. Seaton;K. Reeves
通讯作者：
T. Forbes;D. Seaton;K. Reeves
Petschek 与非局域电阻率重联
影响因子：
2.2
作者：
Baty H
通讯作者：
Baty H