Triggering tearing in a forming current sheet with the mirror instability
Triggering tearing in a forming current sheet with the mirror instability
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DOI：
10.1017/s0022377822000150
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发表时间：
2021-12
影响因子：
2.5
通讯作者：
Himawan W. Winarto;M. Kunz
中科院分区：
文献类型：
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作者：
Himawan W. Winarto;M. Kunz
我们研究的时间依赖性的形成和演化的电流片（CS）在磁化，无碰撞，高β等离子体使用混合动力学粒子在细胞模拟。一个初始撕裂稳定的哈里斯片冻结成一个持续驱动的不可压缩流，使其特征厚度逐渐减少的时间。随着CS变薄，重连场的强度增加，并且流入流体元素中的绝热不变性产生具有过量垂直压力的场偏置压力各向异性。在大的等离子体β，这种各向异性激发镜的不稳定性，这使离子拉莫尔尺度上的重连场变形，并大大降低了CS的有效厚度。撕裂模式的波长与镜子的波长相当，然后变得不稳定，触发更小规模的重联，并在更早的时间比会发生的，如果变薄CS保留其哈里斯轮廓。一种新的方法，用于识别和跟踪X点的介绍，产生的X点分离，最初是在上游等离子体中的垂直和平行的镜面波长之间的中间。这些镜像刺激撕裂模式最终增长和合并产生的CS厚度相媲美的岛宽度，结果，我们验证了在一系列的CS形成时间尺度和初始CS宽度。我们的研究结果可能会发现他们最直接的应用在撕裂破坏的磁褶皱产生的湍流发电机在弱碰撞，高β，天体物理等离子体。
We study the time-dependent formation and evolution of a current sheet (CS) in a magnetised, collisionless, high-beta plasma using hybrid-kinetic particle-in-cell simulations. An initially tearing-stable Harris sheet is frozen into a persistently driven incompressible flow so that its characteristic thickness gradually decreases in time. As the CS thins, the strength of the reconnecting field increases, and adiabatic invariance in the inflowing fluid elements produces a field-biased pressure anisotropy with excess perpendicular pressure. At large plasma beta, this anisotropy excites the mirror instability, which deforms the reconnecting field on ion-Larmor scales and dramatically reduces the effective thickness of the CS. Tearing modes whose wavelengths are comparable to that of the mirrors then become unstable, triggering reconnection on smaller scales and at earlier times than would have occurred if the thinning CS were to have retained its Harris profile. A novel method for identifying and tracking X-points is introduced, yielding X-point separations that are initially intermediate between the perpendicular and parallel mirror wavelengths in the upstream plasma. These mirror-stimulated tearing modes ultimately grow and merge to produce island widths comparable to the CS thickness, an outcome we verify across a range of CS formation timescales and initial CS widths. Our results may find their most immediate application in the tearing disruption of magnetic folds generated by turbulent dynamo in weakly collisional, high-beta, astrophysical plasmas.