受外磁场作用的膨胀细长等离子体云中的多尺度磁场结构
Multi-scale magnetic field structures in an expanding elongated plasma cloud with hot electrons subject to an external magnetic field
摘要：
我们进行3D和2D PIC模拟的磁化等离子体的膨胀，最初均匀地填充半空间，并包含一个半圆柱形区域的加热电子沿等离子体边界的表面拉长。例如，这种几何形状与飞秒激光束在准圆柱形聚焦下对平面目标的烧蚀有关。我们发现非均匀等离子体-真空间断的衰减受平行于其边界的外部磁场的强烈影响。我们观察到各种瞬态现象，包括电子的各向异性散射和随之而来的韦伯不稳定性，并揭示所产生的磁场和电流，包括多个飞离灯丝的z箍缩型和缓慢发展的电流片不同的方向的各种空间结构。自生磁场的大小可以是外部磁场的量级或显著超过外部磁场的量级。这种现象预计将出现在激光和宇宙等离子体中，包括行星磁层和恒星日冕拱中的爆炸过程。
英文摘要：
We carry out 3D and 2D PIC-simulations of the expansion of a magnetized plasma that initially uniformly fills a half-space and contains a semi-cylindrical region of heated electrons elongated along the surface of the plasma boundary. This geometry is related, for instance, to the ablation of a plane target by a femtosecond laser beam under quasi-cylindrical focusing. We find that the decay of the inhomogeneous plasma--vacuum discontinuity is strongly affected by an external magnetic field parallel to its boundary. We observe various transient phenomena, including the anisotropic scattering of electrons and the accompanying Weibel instability, and reveal various spatial structures of the arising magnetic field and current, including multiple flying apart filaments of a z-pinch type and slowly evolving current sheets with different orientations. The magnitude of the self-generated magnetic field can be of the order of or significantly exceed that of the external one. Such phenomena are expected in the laser and cosmic plasmas, including the explosive processes in the planetary magnetospheres and stellar coronal arches.
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