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arXiv 1505.02676physics.space-phastro-ph.SRphysics.plasm-ph
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太阳风终端激波下游的电子分布函数：热电子在哪里？

The electron distribution function downstream of the solar-wind termination shock: Where are the hot electrons?

Hans J. Fahr, John D. Richardson, Daniel Verscharen

备注：
6 pages, 2 figures
发表信息：
Astron. Astrophys. 579, A18, 2015
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摘要：

在大多数关于等离子体冲击波的文献中，电子扮演着“幽灵粒子”的角色，因为它们对质量和动量流的贡献可以忽略不计，并且它们被视为只负责等离子体的电中性。然而，在最近的一些论文中，电子在激波动力学和热力学中，特别是在太阳风终止激波中，扮演了一个新的重要角色。它们以一种非常特殊的方式作用于冲击电场，导致下游电子的超热非平衡分布，这可以用kappa分布函数来表示。在本文中，我们讨论了为什么预期的热电子人口没有看到的旅行者飞船下游的太阳风终止冲击的等离子体探测器。我们表明，热的非平衡电子诱导一个强大的负电荷的任何航天器巡航通过这个下游等离子体环境。这种电荷将航天器探测器上的电子通量降低到无法探测的强度。此外，我们表明，德拜长度$λ_{\mathrm D}^κ$增长到约$λ_{\mathrm D}^κ/λ_{\mathrm D}\simeq 10^{6}$的值相比，在这个热电子环境中的经典值$λ_{\mathrm D}$。这种不寻常的条件允许某种类型的静电等离子体波的传播，在非常大的波长下，允许我们通过这些波的相速度直接确定超热电子的有效温度。在中等波长下，电声色散关系导致非传播振荡，离子等离子体频率$ω_{\mathrm p}$，而不是传统的电子等离子体频率。

英文摘要：

In the majority of the literature on plasma shock waves, electrons play the role of "ghost particles," since their contribution to mass and momentum flows is negligible, and they have been treated as only taking care of the electric plasma neutrality. In some more recent papers, however, electrons play a new important role in the shock dynamics and thermodynamics, especially at the solar-wind termination shock. They react on the shock electric field in a very specific way, leading to suprathermal nonequilibrium distributions of the downstream electrons, which can be represented by a kappa distribution function. In this paper, we discuss why this anticipated hot electron population has not been seen by the plasma detectors of the Voyager spacecraft downstream of the solar-wind termination shock. We show that hot nonequilibrium electrons induce a strong negative electric charge-up of any spacecraft cruising through this downstream plasma environment. This charge reduces electron fluxes at the spacecraft detectors to nondetectable intensities. Furthermore, we show that the Debye length $λ_{\mathrm D}^κ$ grows to values of about $λ_{\mathrm D}^κ/λ_{\mathrm D}\simeq 10^{6}$ compared to the classical value $λ_{\mathrm D}$ in this hot-electron environment. This unusual condition allows for the propagation of a certain type of electrostatic plasma waves that, at very large wavelengths, allow us to determine the effective temperature of the suprathermal electrons directly by means of the phase velocity of these waves. At moderate wavelengths, the electron-acoustic dispersion relation leads to nonpropagating oscillations with the ion-plasma frequency $ω_{\mathrm p}$ , instead of the traditional electron plasma frequency.

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