Electron velocity space hole modes
Electron velocity space hole modes
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电子速度空穴模式
DOI：
10.1029/93ja00433
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发表时间：
1993
影响因子：
--
通讯作者：
R. Richard
中科院分区：
文献类型：
--
作者：
F. Coroniti;M. Ashour‐Abdalla;R. Richard
在空间等离子体中，局部电子分布是由来自不同源区的弹道运动形成的。由于正负平行（v{sub {parallel}}）速度的电子来源不同，与大尺度电磁场的相互作用也不同，因此在v{sub {parallel}} = 0附近的电子分布函数应该具有相当大的结构，包括速度空间空穴的可能性，即相空间密度为零的区域，以及明显的不连续。一种特殊的空穴分布，可能发生在遥远地磁尾的慢激波上游，被证明支持一种非标准等离子体波模式，其频率介于离子和电子等离子体频率之间，平行相速度高于离子，但远低于电子热速度。在低平行速度电子分布中，空穴模式会因斜率为正而失稳，当电子平行温度超过垂直温度时，其生长速率会大大提高；这种模式也可以被热的、快速的离子束激发。空穴模式只存在于磁场方向上一个狭窄的传播角范围内。积分平行分布函数中的不连续也支持非标准波模式，如果分布函数的值在不连续线上增加，则该模式是不稳定的。参30。， 5个无花果。«少
In space plasmas the local electron distribution is formed by ballistic motion from different source regions. Since electrons with positive and negative parallel (v{sub {parallel}}) velocities have different sources and experience different interactions with the large-scale electromagnetic fields, the electron distribution function near v{sub {parallel}} = 0 should possess considerable structure, including the possibility of velocity space holes, i.e., regions where the phase space density is zero, and sharp discontinuities. A particular hole distribution, which may occur upstream of slow shocks in the distant geomagnetic tail, is shown to support a nonstandard plasma wave mode with frequencies between the ion and electron plasma frequencies and parallel phase speed above the ion, but well below the electron, thermal speed. The hole mode can be destabilized by a positive slope in the low parallel velocity electron distribution, and the growth rate is strongly enhanced if the electron parallel temperature exceeds the perpendicular temperature; the mode can also be excited by a hot, fast ion beam. The hole modes exist only for a narrow range of propagation angles about the magnetic field direction. A discontinuity in the integrated parallel distribution function also supports a nonstandard wave mode which is unstable if the valuemore » of the distribution function increases across the discontinuity. 30 refs., 5 figs.« less