Université Grenoble Alpes, Centre National de la Recherche Scientifique-INSU, Institut de Planétologie et d'Astrophysique de Grenoble, F-38041 Grenoble, France.
CEA, DAM, DIF, F-91297 Arpajon, France.
Phys Rev E. 2019 Jul;100(1-1):013205. doi: 10.1103/PhysRevE.100.013205.
In this first paper of a series dedicated to the microphysics of unmagnetized, relativistic collisionless pair shocks, we discuss the physics of the Weibel-type transverse current filamentation instability that develops in the shock precursor, through the interaction of an ultrarelativistic suprathermal particle beam with the background plasma. We introduce in particular the notion of the "Weibel frame," or scattering center frame, in which the microturbulence is of mostly magnetic nature. We calculate the properties of this frame, using first a kinetic formulation of the linear phase of the instability, relying on Maxwell-Jüttner distribution functions, then using a quasistatic model of the nonlinear stage of the instability. Both methods show that (i) the Weibel frame moves at subrelativistic velocities relative to the background plasma, therefore at relativistic velocities relative to the shock front; (ii) the velocity of the Weibel frame relative to the background plasma scales with ξ_{b}, i.e., the pressure of the suprathermal particle beam in units of the momentum flux density incoming into the shock; and (iii) the Weibel frame moves slightly less fast than the background plasma relative to the shock front. Our theoretical results are found to be in satisfactory agreement with the measurements carried out in dedicated large-scale 2D3V particle-in-cell simulations.
在这一系列专门讨论非磁化相对论无碰撞对激波微观物理学的第一篇论文中，我们通过超相对论热粒子束与背景等离子体的相互作用，讨论了在激波前导中发展的 Weibel 型横向电流细丝不稳定性的物理特性。我们特别引入了“Weibel 框架”或散射中心框架的概念，其中微湍流主要具有磁场性质。我们首先使用线性不稳定阶段的动力学公式，依赖于麦克斯韦-朱特纳分布函数，然后使用不稳定性非线性阶段的准静态模型，来计算这个框架的特性。这两种方法都表明：（i）Weibel 框架相对于背景等离子体以亚相对论速度运动，因此相对于激波前缘以相对论速度运动；（ii）Weibel 框架相对于背景等离子体的速度与 ξ_{b}成正比，即超热粒子束的压力以冲击动量通量密度的单位表示；（iii）Weibel 框架相对于激波前缘的运动速度略低于背景等离子体。我们的理论结果与在专门的大规模 2D3V 粒子模拟中进行的测量结果吻合良好。
