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arXiv 1504.01425astro-ph.SRphysics.plasm-ph
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弱电离色球等离子体中的非对称磁重联

Asymmetric Magnetic Reconnection in Weakly Ionized Chromospheric Plasmas

Nicholas A. Murphy, Vyacheslav S. Lukin

摘要:

太阳色球层中磁重联的现实模型必须考虑到等离子体是部分电离的,并且在任何两个经历重联的磁通量束内的等离子体条件可能不相同。当新出现的通量与先前存在的上覆通量相互作用时,色球层中可能发生不对称重联。我们提出了2.5D模拟弱电离的非对称重联,反应等离子体的磁场强度,离子和中性密度,温度是不同的,在每个上游区域。等离子体和中性成分分别演化,以允许非平衡电离。在以前的色球重联模拟中,电流片变薄到中性离子平均自由程的尺度,离子和中性流出强烈耦合。然而,离子和中性流入是不对称解耦的。在磁不对称的情况下,中性粒子从弱场(高密度)上游区域穿过电流片进入强场上游区域的净流动是由中性压力梯度引起的。因此,与外流一起拖曳的中性粒子更有可能来自弱场区域。霍尔效应导致发展的特征四极磁场修改的不对称性,但X点的几何形状预期在霍尔重联不会发生。所有的模拟显示了初始层流阶段后的等离子体团的发展。

英文摘要:

Realistic models of magnetic reconnection in the solar chromosphere must take into account that the plasma is partially ionized and that plasma conditions within any two magnetic flux bundles undergoing reconnection may not be the same. Asymmetric reconnection in the chromosphere may occur when newly emerged flux interacts with pre-existing, overlying flux. We present 2.5D simulations of asymmetric reconnection in weakly ionized, reacting plasmas where the magnetic field strengths, ion and neutral densities, and temperatures are different in each upstream region. The plasma and neutral components are evolved separately to allow non-equilibrium ionization. As in previous simulations of chromospheric reconnection, the current sheet thins to the scale of the neutral-ion mean free path and the ion and neutral outflows are strongly coupled. However, the ion and neutral inflows are asymmetrically decoupled. In cases with magnetic asymmetry, a net flow of neutrals through the current sheet from the weak field (high density) upstream region into the strong field upstream region results from a neutral pressure gradient. Consequently, neutrals dragged along with the outflow are more likely to originate from the weak field region. The Hall effect leads to the development of a characteristic quadrupole magnetic field modified by asymmetry, but the X-point geometry expected during Hall reconnection does not occur. All simulations show the development of plasmoids after an initial laminar phase.

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