对等离子体中斜向无碰撞冲击的密度跃迁:物理解决方案

IF 2.1 3区 物理与天体物理 Q2 PHYSICS, FLUIDS & PLASMAS Journal of Plasma Physics Pub Date : 2024-04-16 DOI:10.1017/s0022377824000370
Antoine Bret, Colby C. Haggerty, Ramesh Narayan
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引用次数: 0

摘要

无碰撞冲击经常使用磁流体力学(MHD)形式分析,尽管 MHD 假设平均自由路径很小。然而,压力的各向同性是二元碰撞的结果,也是 MHD 的假设,但在无碰撞冲击中可能并不适用。在磁化等离子体中尤其如此,磁场可以稳定各向异性。在之前的一篇文章(Bret & Narayan, J. Plasma Phys., vol. 88, no.该模型可以解决相对于冲击前沿的任何方向的场。然而,对于某些上游参数值,我们发现了几个下游解。在此,我们通过展示如何从代数提供的解中选出物理解,完成了布雷特 & 纳拉扬(《等离子体物理》,第 88 卷,第 6 期,2022b,第 905880615 页)开始的工作。这可以通过两种方法实现:(i) 选择下游场斜度与上游场斜度最接近的解。这一标准在并行情况下得到体现,并得到了粒子入胞模拟的支持。(ii) 筛选出不符合 MHD 多解修剪标准的解,即我们假定在无碰撞情况下有效的演化性标准。最终得出的结果是,给定的上游构型会产生唯一的下游构型,或者没有下游构型(如 MHD)。在平行冲击的情况下,与 MHD 的偏离最大。
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Density jump for oblique collisionless shocks in pair plasmas: physical solutions

Collisionless shocks are frequently analysed using the magnetohydrodynamics (MHD) formalism, even though MHD assumes a small mean free path. Yet, isotropy of pressure, the fruit of binary collisions and assumed in MHD, may not apply in collisionless shocks. This is especially true within a magnetized plasma, where the field can stabilize an anisotropy. In a previous article (Bret & Narayan, J. Plasma Phys., vol. 88, no. 6, 2022b, p. 905880615), a model was presented capable of dealing with the anisotropies that may arise at the front crossing. It was solved for any orientation of the field with respect to the shock front. Yet, for some values of the upstream parameters, several downstream solutions were found. Here, we complete the work started in Bret & Narayan (J. Plasma Phys., vol. 88, no. 6, 2022b, p. 905880615) by showing how to pick the physical solution out of the ones offered by the algebra. This is achieved by 2 means: (i) selecting the solution that has the downstream field obliquity closest to the upstream one. This criterion is exemplified on the parallel case and backed up by particle-in-cell simulations. (ii) Filtering out solutions which do not satisfy a criteria already invoked to trim multiple solutions in MHD: the evolutionarity criterion, that we assume valid in the collisionless case. The end result is a model in which a given upstream configuration results in a unique, or no downstream configuration (as in MHD). The largest departure from MHD is found for the case of a parallel shock.

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来源期刊
Journal of Plasma Physics
Journal of Plasma Physics 物理-物理:流体与等离子体
CiteScore
3.50
自引率
16.00%
发文量
106
审稿时长
6-12 weeks
期刊介绍: JPP aspires to be the intellectual home of those who think of plasma physics as a fundamental discipline. The journal focuses on publishing research on laboratory plasmas (including magnetically confined and inertial fusion plasmas), space physics and plasma astrophysics that takes advantage of the rapid ongoing progress in instrumentation and computing to advance fundamental understanding of multiscale plasma physics. The Journal welcomes submissions of analytical, numerical, observational and experimental work: both original research and tutorial- or review-style papers, as well as proposals for its Lecture Notes series.
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