Effect of Guiding Field to Low-Frequency Electromagnetic Instabilities in the Collisionless Current Sheet
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摘要: 通过数值求解无碰撞电流片中可压缩磁流体力学模型下得到的一般形式的色散关系,讨论了无碰撞电流片中引导场对低频电磁波不稳定性的影响.结果表明,平衡态磁场中的引导场,对于三维扰动传播的波不稳定性有很强的影响.(1)在电流片中间平面上(z=0),无引导场时,没有不稳定性发生,但若存在引导场,不稳定性便发生,并随着引导场的增强,不稳定性明显增强,不稳定的波模可能是低混杂模.(2)在中间平面附近(z=0.2),电流片是不稳定的.随着引导场的增强,不稳定性增长率明显地增强,不稳定的波模从平行和反平行两个方向传播变为反平行方向一个方向传播,并且是斜传播的,具有低频哨声模或低混杂模的特征.(3)在电流片边缘附近(z=0.8),引导场对不稳定的波模和增长率没有明显影响,不稳定的波模都是准平行的哨声波.Abstract: This paper discuss the effect of guiding field to low-frequency electromagnetic instabilities in the collisionless current sheet with the dispersion relation obtained by collisionless and compressible magnetohydrodynamic model. The results show the guiding field affects on the three-dimensional disturbed propagation waves strongly. （1） On the middle plane of current sheet （z = 0）, if there is not guiding field, no instability observed, but if there is guiding field, instabilities can take place. （2） Near the middle of current sheet （z = 0.2）, the current sheet is instable. With increasing of guiding field, the grow rate increased obviously. The wave mode may be whistler or low-hybrid wave. （3） Near the edge of current sheet （z = 0.8）, the effect of guiding field become not clearly. The instability wave mode is quasi-parallel propagation whistler.
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Key words:
- Collisionless current sheet /
- Guiding field /
- Wave instability /
- Dispersion relation
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