Cold ions in the hot plasma sheet of Earth's magnetotail
Cold ions in the hot plasma sheet of Earth's magnetotail
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DOI：
10.1038/nature01502
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发表时间：
2003-04
期刊：
影响因子：
64.8
通讯作者：
K. Seki;M. Hirahara;M. Hoshino;T. Terasawa;R. Elphic;Yoshifumi Saito;T. Mukai;H. Hayakawa;H. Kojima;H. Matsumoto
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文献类型：
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作者：
K. Seki;M. Hirahara;M. Hoshino;T. Terasawa;R. Elphic;Yoshifumi Saito;T. Mukai;H. Hayakawa;H. Kojima;H. Matsumoto
宇宙中大多数可见的物质都以等离子体的形式存在。该等离子体如何被加热，特别是初始非平衡等离子体分布如何松弛至热平衡（如麦克斯韦-波尔兹曼统计所预测的），是天体物理学和实验室等离子体研究中的一个基本问题。天体物理等离子体通常是如此的稀薄，以至于二元碰撞可以忽略不计，并且不清楚这些“无碰撞”等离子体的热平衡是如何发展的。无碰撞等离子体的一个例子是地球的等离子体片，在那里已经观察到离子温度约为5 × 107 K的热化热等离子体。在这里，我们报告的等离子体分布函数在日食的直接观测，揭示了冷离子在地球的等离子体片与热化热离子共存。这种冷成分不能被卫星上的等离子体传感器检测到，这些传感器在阳光下带正电，但我们在地球阴影中的观测表明，冷离子的密度与热离子的密度相当。这种高密度在现有的理论中很难解释，因为它需要一种机制，允许一半的源等离子体在进入热湍流等离子体片时保持冷却。
Most visible matter in the Universe exists as plasma. How this plasma is heated, and especially how the initial non-equilibrium plasma distributions relax to thermal equilibrium (as predicted by Maxwell–Boltzman statistics), is a fundamental question in studies of astrophysical,,and laboratory plasmas,. Astrophysical plasmas are often so tenuous that binary collisions,can be ignored, and it is not clear how thermal equilibrium develops for these ‘collisionless’ plasmas. One example of a collisionless plasma is the Earth's plasma sheet, where thermalized hot plasma with ion temperatures of about 5 × 107K has been observed. Here we report direct observations of a plasma distribution function during a solar eclipse, revealing cold ions in the Earth's plasma sheet in coexistence with thermalized hot ions. This cold component cannot be detected by plasma sensors on satellites that are positively charged in sunlight, but our observations in the Earth's shadow show that the density of the cold ions is comparable to that of hot ions. This high density is difficult to explain within existing theories,,, as it requires a mechanism that permits half of the source plasma to remain cold upon entry into the hot turbulent plasma sheet.