The Kelvin–Helmholtz instability in weakly ionized plasmas – II. Multifluid effects in molecular clouds
The Kelvin–Helmholtz instability in weakly ionized plasmas – II. Multifluid effects in molecular clouds
复制标题
弱电离等离子体中的开尔文-亥姆霍兹不稳定性——分子云中的多流体效应
DOI：
--
复制
发表时间：
2011
期刊：
影响因子：
--
通讯作者：
T. Downes
中科院分区：
文献类型：
--
作者：
A. C. Jones;T. Downes
我们研究了弱电离多流体磁流体(MHD)等离子体中的开尔文-亥姆霍兹不稳定性，其参数与典型分子云的参数相匹配。这种不稳定性能够将有序流动转化为无序流动。因此，它可能能够将例如恒星喷流的弓形激波中的能量转化为分子云中的湍流能量。由于这些云是弱电离的，理想的MHD近似不适用于大约十分之一秒或更小的尺度。本文推广了Jones&Downes关于多流体MHD效应下开尔文-亥姆霍兹不稳定性演化的工作。在适用于分子云的物理参数下，双极扩散的这些效应和霍尔效应被一起研究。我们将注意力局限于具有跨音速但超Alfv‘enic速度跳跃的单个剪切层的情况，并且选择计算域来匹配不稳定性的线性最快增长模式的波长。我们发现，虽然多流体效应的引入并不影响不稳定性的线性增长率，但非线性行为发生了相当大的变化。由于双极扩散，磁场与体流是解耦的，这导致了磁场演化的显著不同。预计霍尔效应将导致垂直于平面的磁力线发生明显的重新定向。然而，结果表明，与双极扩散相结合，可以令人惊讶地有效地抑制这种效应。
We present a study of the Kelvin–Helmholtz instability in a weakly ionized, multifluid magnetohydrodynamic (MHD) plasma with parameters matching those of a typical molecular cloud. The instability is capable of transforming well-ordered flows into disordered flows. As a result, it may be able to convert the energy found in, for example, bowshocks from stellar jets into the turbulent energy found in molecular clouds. As these clouds are weakly ionized, the ideal MHD approximation does not apply at scales of around a tenth of a parsec or less. This paper extends the work of Jones & Downes on the evolution of the Kelvin–Helmholtz instability in the presence of multifluid MHD effects. These effects of ambipolar diffusion and the Hall effect are here studied together under physical parameters applicable to molecular clouds. We restrict our attention to the case of a single shear layer with a transonic, but super-Alfv´ enic, velocity jump and the computational domain is chosen to match the wavelength of the linearly fastest growing mode of the instability. We find that while the introduction of multifluid effects does not affect the linear growth rates of the instability, the non-linear behaviour undergoes considerable change. The magnetic field is decoupled from the bulk flow as a result of the ambipolar diffusion, which leads to a significant difference in the evolution of the field. The Hall effect would be expected to lead to a noticeable re-orientation of the magnetic field lines perpendicular to the plane. However, the results reveal that the combination with ambipolar diffusion leads to a surprisingly effective suppression of this effect.