磁尾静电离子束流-密度漂移不稳定性的数值研究

Numerical Study of Electrostatic Ion Beam-Density Drift Instabilities in the Geomagnetic Tail

本文研究了磁尾等离子体片边界层宽频带静电噪声的产生机制.模型等离子体由暖的背景电子、暖的向地球方向的离子束流和较冷的向尾方向的离子束流组成.结果表明,静电离子束流-密度漂移不稳定性可以在比较宽的频率范围内激发,在低频区大传播角方向上增长率最大,在高频区小传播角方向上增长率也比较大。最大增长率的方向取决于离子束流和密度漂移的速度比值.这些结果与磁尾观测到的宽频带静电噪声特征符合一致.

The mechanism of the generation of the broadband electrostatic noises (BEN) in the plasma sheet boundary layer is studied in this paper. The model plasma consists of warm background electrons, warm earthward ion beams and cold tailward ion beams. It is shown that electrostatic ion beam-density drift instabilities can be excited in the broad range of the frequency, the peak growth rate is found in the low frequency region at the large propagation angle, and the considerable growth rate in the high frequency region at the small propagation angle. The direction for the peak growth rate is determined by the ratio of the ion beam velocity to the density gradient drift velocity. The results are consistent with observations of the magnetotail' BEN.