无碰撞激波上游低频波的激发及其对激波耗散机制的影响

由于很大一部分来自激波上游的粒子被激波面所反射，因此在准平行无碰撞激波的上游存在着等离子体束流．通过一维混合模拟方法，计算了束流密度较小(nb／n0=0．02)和较大(nb／n0=0．2)两种不同情形下的等离子体束流不稳定性．结果表明，在束流密度较小时，束流激发的主要是平行于背景磁场方向传播的右旋波，此波动只能对束流粒子产生影响，包括减速和加热．在束流密度较大时，束流可同时激发平行和反平行于背景磁场方向传播的右旋波，除能对束流粒子产生影响外，还可通过非共振作用加速和加热背景粒子．文中对准平行无碰撞激波耗散机制的影响也进行了讨论。

Excited Low Frequency Waves by Beam Plasma in Upstream of Collisionless Shock and Their Effect on Dissipation of Shock

Due to the reflection by collisonless shock, ion beam can be formed in upstream of collisionless shock. In this paper, a one-dimensional hybrid simulation is performed to investigate beam plasma instabilities for two cases: low (nb/n0= 0.02) and high (nb/n0 = 0.2) beam densities, where rib and n0 represents the beam and background plasma density respectively. The results show that for low beam density the beam mainly excites the right-polarized waves through resonance interaction. The waves propagate parallel to the ambient magnetic field, and they can only decelerate a.nd heat the beam protons. When the beam density is high, the beam can excite the waves with propagation direction parallel and anti-parallel to the ambient magnetic field. These waves can interact with beam protons relying on resonance condition, while they interact with background protons due to non-resonant effects. Besides decelerating and heating the beam protons, they can also accelerate and heat the background protons. Their effects on the dissipation of quasi-parallel collisionless shock are also discussed.