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arXiv 1503.05260astro-ph.SRphysics.plasm-phphysics.space-ph
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离子质量变化和磁畴尺寸对无碰撞磁重联中八极面外磁场产生的影响

The effects of ion mass variation and domain size on octupolar out-of-plane magnetic field generation in collisionless magnetic reconnection

Jan Graf von der Pahlen, David Tsiklauri

备注：
Published in Physics of Plasmas. arXiv admin note: text overlap with arXiv:1406.3890
发表信息：
Phys. Plasmas 22, 032905 (2015)
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摘要：

J. Graf von der Pahlen和D. Tsiklauri，Phys. Plas. 21，060705（2014）确定了在受应力的$X$点塌陷中八极面外磁场结构的产生是由于离子电流。场具有中心区域，包括众所周知的四极场（四极分量），以及更靠近域的角的四个极性相反的附加极（八极分量）。在这项扩展的工作中，八极结构的依赖域的大小和离子质量的变化进行了研究。模拟结果表明，产生的八极磁场的强度和空间结构与离子电子质量比无关。从而表明，离子电流在物理现实场景中的平面外磁结构生成中起着重要作用。对不同系统尺寸的模拟表明，八极结构的宽度保持不变，其空间范围为离子惯性长度的数量级。因此，结构的宽度似乎与边界条件的影响无关。然而，八极结构的长度增加更大的域的大小，由外部系统的大小规定。发现这是流出区域中的面内磁场的结构停止颗粒流并因此终止产生面外场的面内电流的结果。八极磁场结构的产生也建立在撕裂模式重联的情况。讨论了八极场产生的差异以及由此产生的$X$点坍塌和撕裂模式之间的定性差异。

英文摘要：

J. Graf von der Pahlen and D. Tsiklauri, Phys. Plas. 21, 060705 (2014), established that the generation of octupolar out-of-plane magnetic field structure in a stressed $X$-point collapse is due to ion currents. The field has a central region, comprising of the well-known qaudrupolar field (quadrupolar components), as well as four additional poles of reversed polarity closer to the corners of the domain (octupolar components). In this extended work, the dependence of the octupolar structure on domain size and ion mass variation is investigated. Simulations show that the strength and spatial structure of the generated octupolar magnetic field is independent of ion to electron mass ratio. Thus showing that ion currents play a significant role in out-of-plane magnetic structure generation in physically realistic scenarios. Simulations of different system sizes show that the width of the octupolar structure remains the same and has a spacial extent of the order of the ion inertial length. The width of the structure thus appears to be independent on boundary condition effects. The length of the octupolar structure however increases for greater domain sizes, prescribed by the external system size. This was found to be a consequence of the structure of the in-plane magnetic field in the outflow region halting the particle flow and thus terminating the in-plane currents that generate the out-of-plane field. The generation of octupolar magnetic field structure is also established in a tearing-mode reconnection scenario. The differences in the generation of the octupolar field and resulting qualitative differences between $X$-point collapse and tearing-mode are discussed.

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