Blackett Laboratory, Imperial College London, South Kensington, United Kingdom.
Phys Rev Lett. 2011 Nov 18;107(21):215002. doi: 10.1103/PhysRevLett.107.215002. Epub 2011 Nov 14.
Shock waves are ubiquitous in space and astrophysics. They transform directed flow energy into thermal energy and accelerate energetic particles. The energy repartition is a multiscale process related to the spatial and temporal structure of the electromagnetic fields within the shock layer. While large scale features of ion heating are known, the electron heating and smaller scale fields remain poorly understood. We determine for the first time the scale of the electron temperature gradient via electron distributions measured in situ by the Cluster spacecraft. Half of the electron heating coincides with a narrow layer several electron inertial lengths (c/ω(pe)) thick. Consequently, the nonlinear steepening is limited by wave dispersion. The dc electric field must also vary over these small scales, strongly influencing the efficiency of shocks as cosmic ray accelerators.
冲击波在空间和天体物理学中无处不在。它们将定向流动能量转化为热能，并加速高能粒子。能量分配是一个与冲击波层内电磁场的时空结构有关的多尺度过程。虽然人们已经了解了离子加热的大尺度特征，但电子加热和较小尺度的场仍然知之甚少。我们首次通过Cluster 航天器原位测量的电子分布来确定电子温度梯度的尺度。一半的电子加热与一个只有几个电子惯性长度（c/ω(pe)）厚的狭窄层重合。因此，非线性陡化受到波色散的限制。直流电场也必须在这些小尺度上变化，这强烈影响着冲击波作为宇宙射线加速器的效率。
