Modelling of magnetic interactions in partially-ionized gas: application to the FIP effect
Modelling of magnetic interactions in partially-ionized gas: application to the FIP effect
复制标题
部分电离气体中磁相互作用的建模：在 FIP 效应中的应用
DOI：
10.1023/a:1005096325238
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发表时间：
1998
期刊：
影响因子：
2.8
通讯作者：
D. Mullan
中科院分区：
文献类型：
--
作者：
C. Arge;D. Mullan
我们已经修改了Zeus代码来模拟部分电离气体中的磁相互作用。当两个极性相反的区域相互接触时，响应洛伦兹力的漂移离子落入磁场的极小值，然后漂移的离子迫使中性粒子参与流动。由于发生离子-原子碰撞所需的时间有限，从相互作用位置出来的气体的离子/原子比可能会相对于周围介质中的离子/原子比发生变化。为了模拟这种效应，我们将Zeus程序修改为两步迭代过程，涉及程序的流体力学(HD)和磁流体动力学(MHD)版本之间的循环。离子流体和原子流体通过碰撞耦合在一起。我们的模拟表明，在色球条件下，流出气体的离子/原子比增加了10倍或更多。增强的大小取决于两个关键的比率：电离度(Ni/NA)和等离子体β参数。我们表明，在我们提出的机制的背景下，太阳色球中离子/原子增强的幅度受到显著的自我调节，因为离子密度ni在我们感兴趣的高度范围内几乎不变。我们的结果在太阳的背景下是相关的，在太阳的背景下，具有低第一电离势(FIP)的元素的日冕丰度在某些磁结构中被系统地增强。虽然太阳以外的恒星的数据很稀少，但我们指出，我们的结果对于解释现有的恒星数据也很有用。
We have adapted the ZEUS code to model magnetic interactions in partially ionized gas. When two regions of opposite polarity come into contact with each other, ions drifting in response to the Lorentz force fall into the minimum of the magnetic field, and then the drifting ions force the neutrals to take part in the flow. Because of the finite time required for ion-atom collisions to occur, the gas which emerges from the interaction site has an ion/atom ratio which may be altered relative to that in the ambient medium. In order to model this effect, we adapt the Zeus code to a two-step iterative process involving a cycle between the hydrodynamic (HD) and the magnetohydrodynamic (MHD) versions of the code. The ion and atom fluids are coupled by collisions. Our simulations show that in chromospheric conditions, outflowing gas exhibits enhancements in ion/atom ratios which may be as large as a factor of 10 or more. The magnitude of the enhancements is determined by two key ratios which enter into the problem: the degree of ionization (ni/na), and the plasma β parameter. We show that, in the context of the mechanism we propose here, the amplitude of the ion/atom enhancements in the solar chromosphere is subject to a remarkable self-regulation because the ion density ni is almost invariant over the height range of interest to us. Our results are relevant in the context of the Sun, where the coronal abundances of elements with low first ionization potential (FIP) are systematically enhanced in certain magnetic structures. Although data for stars other than the Sun are sparse, we point out that our results are also useful for interpreting the available stellar data.