arXiv 1307.19632013-07-08physics.space-phphysics.plasm-ph

非均匀初始环境和引导场对等离子体团不稳定性的影响

Effects of the non-uniform initial environment and the guide field on the plasmoid instability

Lei Ni, Jun Lin, Nicholas A. Murphy

发表信息：: Phys. Plasmas 20, 061206(2013)
DOI：: 10.1063/1.4811144

摘要：

通过2.5维电阻磁流体动力学（MHD）模拟研究了非均匀初始质量密度和温度对等离子体团不稳定性的影响。结果表明，当电流片中心的初始等离子体密度高于上游区域时，等离子体团不稳定性的发展被明显阻止。因此，中心处的等离子体密度越高，上游区域的等离子体$β$越低，触发二次不稳定性所需的临界Lundquist数越高。当为$β=0.2$时，临界Lundquist数大于$10^4$。对于相同的伦德奎斯特数，磁重联率较低的等离子体$β$的情况下。而当初始质量密度较均匀且Lundquist数较小时，低等离子体$β$的磁重联率较高.对于初始质量密度均匀的高Lundquist数情形（$>10^4$），磁重联不受初始等离子体$β$和温度分布的影响。我们的研究结果表明，在电阻MHD中，引导场对等离子体团不稳定性的影响是有限的。

英文摘要：

Effects of non-uniform initial mass density and temperature on the plasmoid instability are studied via 2.5-dimensional resistive magnetohydrodynamic(MHD) simulations. Our results indicate that the development of the plasmoid instability is apparently prevented when the initial plasma density at the center of the current sheet is higher than that in the upstream region. As a result, the higher the plasma density at the center and the lower the plasma $β$ in the upstream region, the higher the critical Lundquist number needed for triggering secondary instabilities. When $β=0.2$, the critical Lundquist number is higher than $10^4$. For the same Lundquist number, the magnetic reconnection rate is lower for the lower plasma $β$ case. Oppositely, when the initial mass density is uniform and the Lundquist number is low, the magnetic reconnection rate turns out to be higher for the lower plasma $β$ case. For the high Lundquist number case ($>10^4$) with uniform initial mass density, the magnetic reconnection is not affected by the initial plasma $β$ and the temperature distribution. Our results indicate that the guide field has a limited impact on the plasmoid instability in resistive MHD.

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