分子云中的带电粒子和Kelvin Helmholtz不稳定性
Charged grains and Kelvin Helmholtz instability in molecular clouds
摘要：
尘埃颗粒的存在深刻地影响了分子云中磁场的扩散。当电子和离子与磁场耦合良好，而带电粒子仅为间接耦合时，在部分电离的尘埃云中，出现的霍尔扩散可能超过所有其他非理想磁流体动力学（MHD）效应。低频、长波长（0.01 ~ 0.1 pc）色散MHD波将在这样的介质中传播，波的偏振由尘埃电荷密度或尘埃尺寸分布决定。在剪切流的存在下，这些波可能成为开尔文亥姆霍兹（KH）不稳定的粉尘电荷密度或粒度分布作为一个开关的不稳定性。当霍尔扩散时间是长的（相比的时间超过波被剪切），在亚Alfvenic流的存在下的不稳定性的增长率增加与晶粒上的电荷数Z，而它是淬火在Alfvenic或超Alfvenic流的存在下。然而，当霍尔扩散是快速的，不稳定性的增长率仅间接依赖于尘埃电荷。
英文摘要：
The presence of dust grains profoundly affects the diffusion of the magnetic field in molecular clouds. When the electrons and ions are well coupled to the magnetic field and charged grains are only indirectly coupled, emergent Hall diffusion may dominate over all the other non ideal magnetohydrodynamic (MHD) effects in a partially ionized dusty cloud. The low frequency, long wavelength (0.01 t0 1 pc) dispersive MHD waves will propagate in such a medium with the polarization of the waves determined by the dust charge density or the dust size distribution. In the presence of shear flows, these waves may become Kelvin Helmholtz (KH) unstable with the dust charge density or the grain size distribution operating as a switch to the instability. When Hall diffusion time is long (compared to the time over which waves are sheared), the growth rate of the instability in the presence of sub Alfvenic flow increases with the charge number Z on the grain, while it is quenched in the presence of Alfvenic or super Alfvenic flows. However, when Hall diffusion is fast, the growth rate of the instability depends on the dust charge only indirectly.
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