Collisionless shock formation, spontaneous electromagnetic fluctuations, and streaming instabilities
Collisionless shock formation, spontaneous electromagnetic fluctuations, and streaming instabilities
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DOI：
10.1063/1.4798541
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发表时间：
2013-04-01
影响因子：
2.2
通讯作者：
Silva, L. O.
中科院分区：
文献类型：
--
作者：
Bret, A.;Stockem, A.;Silva, L. O.
无碰撞冲击在天体物理学和实验室中无处不在。最近的数值模拟和实验表明，它们是如何从两个无碰撞的等离子体壳的相遇中产生的。当壳层相互穿透时，重叠区域变得不稳定，触发了激波的形成。作为对该过程的微观理解的第一步，我们在这里详细分析了初始不稳定阶段。一方面，在两个对称的初始冷对等离子体碰撞的情况下进行2D相对论粒子模拟。另一方面，分析了工作中的不稳定性，以及饱和场和被放大的种子场。对于温和的相对论运动和向前，韦伯模式支配线性相位。我们推导出的线性相位的持续时间与模拟吻合良好的表达式。这个饱和时间实际上构成了激波形成时间的下限。(C)2013年美国物理学会。[http：//dx.doi.org/10.1063/1.4798541]
Collisionless shocks are ubiquitous in astrophysics and in the lab. Recent numerical simulations and experiments have shown how they can arise from the encounter of two collisionless plasma shells. When the shells interpenetrate, the overlapping region turns unstable, triggering the shock formation. As a first step towards a microscopic understanding of the process, we analyze here in detail the initial instability phase. On the one hand, 2D relativistic Particle-In-Cell simulations are performed where two symmetric initially cold pair plasmas collide. On the other hand, the instabilities at work are analyzed, as well as the field at saturation and the seed field which gets amplified. For mildly relativistic motions and onward, Weibel modes govern the linear phase. We derive an expression for the duration of the linear phase in good agreement with the simulations. This saturation time constitutes indeed a lower-bound for the shock formation time. (C) 2013 American Institute of Physics. [http://dx.doi.org/10.1063/1.4798541]