Nonthermal particle acceleration in shock front region: "Shock surfing accelerations"
Nonthermal particle acceleration in shock front region: "Shock surfing accelerations"
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DOI：
10.1143/ptps.143.149
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发表时间：
2001-01-01
影响因子：
--
通讯作者：
Hoshino, M
中科院分区：
文献类型：
--
作者：
Hoshino, M
据信，超热粒子加速以及等离子体热化通过粒子与各种等离子体不稳定性激发的静电和电磁波的相互作用而发生在无碰撞激波前沿区域附近。本文通过关注粒子与激波前沿区/激波过渡层中形成的大幅度孤立波的相互作用，讨论了垂直磁声激波的超热粒子加速。激波前沿区域被认为是高度湍流的，但除了这种湍流之外，现代卫星在地球弓激波中观测到了一系列嵌入激波过渡层中的大振幅、小尺度孤立波。受小尺度孤立波发现的启发，我们通过使用细胞内粒子模拟来研究它们对粒子加速度的影响。我们首先研究一种由离子和电子组成的非相对论高马赫数激波。我们发现，离子电子激波中的静电孤立波是由入射电子和激波前沿反射离子之间的双流不稳定性激发的。我们讨论了孤立波捕获的电子可以与激波过渡层中的激波运动电场共振，所谓的激波冲浪机制对于产生非热高能电子是有效的。我们证明，当阿尔文马赫数 M-A 超过 10（接近 100）时，被捕获的电子可以加速到由全局激波大小决定的激波势能。接下来，我们研究等离子体成分由电子和正电子组成的相对论激波，即对等离子体。我们讨论了磁声孤立波可以代替离子电子激波中的静电孤立波。随着上游坡印亭通量与上游动能通量之比西格玛的减小，磁声孤波在激波过渡层中形成电流片，从而将粒子捕获在磁零区中。我们讨论了相对论性电子-正电子激波中的激波冲浪加速是在磁声孤波捕获的粒子与激波运动电场的相互作用下发生的。被捕获的粒子可以被有效地加速到由全局激波大小确定的激波势能。
It is believed that the supra-thermal particle acceleration as well as the plasma thermalization occurs in the neighborhood of collisionless shock front regions through the interaction of particles with the electrostatic and electromagnetic waves excited by a wide variety of plasma instabilities. In this paper, supra-thermal particle acceleration for a perpendicular magnetosonic shock is discussed by focusing on the interaction of particles with a large amplitude solitary wave formed in the shock front region/shock transition layer. The shock front region was thought to be highly turbulent, but in addition to such a turbulence, a series of large-amplitude, small-scale solitary waves embedded in the shock transition layer are observed by the modern satellites' observations in the earth's bow shock. Motivated by the discovery of the small-scale solitary waves, we study their effect on the particle acceleration by using the particle-in-cell simulations. We study first a non-relativistic, high Mach number shock whose composition consists of ion and electron. We find that the electrostatic solitary waves are excited in the ion-electron shocks by a two-stream instability between the incoming electrons and the reflected ions from the shock front. We discuss that the electrons trapped by the solitary wave can resonate with the shock motional electric field in the shock transition layer, and the so-called shock surfing mechanism is effective for producing the non-thermal, high-energy electrons. We show that the trapped electron can be accelerated up to the shock potential energy determined by a global shock size when the Alfven Mach number M-A exceeds 10 similar to 100. Next we investigate a relativistic shock whose plasma composition consists of electron and positron, i.e., pair plasma. We discuss that a magnetosonic solitary wave can take the place of the electrostatic solitary wave in the ion-electron shocks. As decreasing sigma of the ratio of the upstream Poyinting flux to the upstream kinetic energy flux, the magnetosonic solitary wave forms the current sheet in the shock transition layer, which in turn can trap the particles in the magnetic null region. We discuss that the shock surfing acceleration in a relativistic electron-positron shock occurs under the interaction of the trapped particles by the magnetosonic solitary wave with the shock motional electric field. The trapped particle can be efficiently accelerated up to the shock potential energy determined by a global shock size.