Density jump as a function of magnetic field for collisionless shocks in pair plasmas: The perpendicular case
Density jump as a function of magnetic field for collisionless shocks in pair plasmas: The perpendicular case
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DOI：
10.1063/1.5099000
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发表时间：
2019-05
影响因子：
2.2
通讯作者：
A. Bret;Ramesh Narayan
中科院分区：
文献类型：
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作者：
A. Bret;Ramesh Narayan
在没有频繁的二元碰撞来各向同性等离子体的情况下，通过无碰撞冲击来满足磁流体动力学（MHD）朗肯-雨果尼奥特跳跃条件并非易事。特别是，外部磁场的存在下，可以允许稳定的各向异性，这意味着一些偏离各向同性MHD跳跃。这种各向异性在磁场方面的函数依赖性尚待确定。通过假设等离子体通过激波阵面的动力学历史，我们最近设计了一个关于下游各向异性的理论，从而根据平行激波的场强设计了密度跳跃的理论[A. Bret和R. Narayan，J. Plasma Phys. 84，905840604（2018）]。在这里，我们将分析扩展到垂直激波的情况。我们仍然发现，该领域减少了密度跳跃，但效果是不太明显的比在平行的cases.In频繁的二元碰撞的情况下，各向同性的等离子体，磁流体动力学（MHD）的朗肯-Hugoniot跳跃条件的实现碰撞冲击是不平凡的。特别是，外部磁场的存在下，可以允许稳定的各向异性，这意味着一些偏离各向同性MHD跳跃。这种各向异性在磁场方面的函数依赖性尚待确定。通过假设等离子体通过激波阵面的动力学历史，我们最近设计了一个关于下游各向异性的理论，从而根据平行激波的场强设计了密度跳跃的理论[A. Bret和R. Narayan，J. Plasma Phys. 84，905840604（2018）]。在这里，我们将分析扩展到垂直激波的情况。我们仍然发现，该领域减少了密度跳跃，但效果是不太明显，比在平行的情况下。
In the absence of frequent binary collisions to isotropize the plasma, the fulfillment of the magnetohydrodynamic (MHD) Rankine–Hugoniot jump conditions by collisionless shocks is not trivial. In particular, the presence of an external magnetic field can allow for stable anisotropies, implying some departures from the isotropic MHD jumps. The functional dependence of such anisotropies in terms of the field is yet to be determined. By hypothesizing a kinetic history of the plasma through the shock front, we recently devised a theory of the downstream anisotropy, hence of the density jump, in terms of the field strength for a parallel shock [A. Bret and R. Narayan, J. Plasma Phys. 84, 905840604 (2018)]. Here, we extend the analysis to the case of a perpendicular shock. We still find that the field reduces the density jump, but the effect is less pronounced than in the parallel case.In the absence of frequent binary collisions to isotropize the plasma, the fulfillment of the magnetohydrodynamic (MHD) Rankine–Hugoniot jump conditions by collisionless shocks is not trivial. In particular, the presence of an external magnetic field can allow for stable anisotropies, implying some departures from the isotropic MHD jumps. The functional dependence of such anisotropies in terms of the field is yet to be determined. By hypothesizing a kinetic history of the plasma through the shock front, we recently devised a theory of the downstream anisotropy, hence of the density jump, in terms of the field strength for a parallel shock [A. Bret and R. Narayan, J. Plasma Phys. 84, 905840604 (2018)]. Here, we extend the analysis to the case of a perpendicular shock. We still find that the field reduces the density jump, but the effect is less pronounced than in the parallel case.