动态准垂直激波：星系团的发现
The dynamic quasiperpendicular shock: Cluster discoveries
摘要：
无碰撞冲击物理学是一个非常广泛的课题，已经研究了五十多年。然而，仍有一些重要问题尚未解决。准垂直激波中粒子群间的能量再分配是一个多尺度过程，与激波层内电磁场的时空结构有关。最重要的过程发生在主磁过渡或斜坡区附近。在这个区域中的电磁场的分布决定了离子反射的特性，从而定义了离子加热和超临界冲击的能量耗散的条件，并且也定义了发生电子加热的重要部分的区域。所有这些过程都取决于斜坡和底部区域的特征空间尺度，只要激波是静止的。对无碰撞激波的最早研究发现，非线性、耗散和色散是阻止激波转变变陡的过程。它们的相对作用决定了电场和磁场的尺度，从而控制了诸如离子反射、电子加热和粒子加速等过程的特性。这篇评论的目的是解决一个子集的未解决的问题，在无碰撞冲击物理从实验的角度来看，利用多点观测星上集群。我们解决的问题是场的尺度和电子加热的尺度的确定，前兆波列能量源的识别，通过测量短尺度波场估计异常电阻率在能量耗散过程中的作用，以及在一次冲击波阵面穿越过程中直接观测重整过程。
英文摘要：
The physics of collisionless shocks is a very broad topic which has been studied for more than five decades. However, there are a number of important issues which remain unresolved. The energy repartition amongst particle populations in quasiperpendicular shocks is a multi-scale process related to the spatial and temporal structure of the electromagnetic fields within the shock layer. The most important processes take place in the close vicinity of the major magnetic transition or ramp region. The distribution of electromagnetic fields in this region determines the characteristics of ion reflection and thus defines the conditions for ion heating and energy dissipation for supercritical shocks and also the region where an important part of electron heating takes place. All of these processes are crucially dependent upon the characteristic spatial scales of the ramp and foot region provided that the shock is stationary. The earliest studies of collisionless shocks identified nonlinearity, dissipation, and dispersion as the processes that arrest the steepening of the shock transition. Their relative role determines the scales of electric and magnetic fields, and so control the characteristics of processes such as of ion reflection, electron heating and particle acceleration. The purpose of this review is to address a subset of unresolved problems in collisionless shock physics from experimental point of view making use multi-point observations onboard Cluster satellites. The problems we address are determination of scales of fields and of a scale of electron heating, identification of energy source of precursor wave train, an estimate of the role of anomalous resistivity in energy dissipation process by means of measuring short scale wave fields, and direct observation of reformation process during one single shock front crossing.
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