MAGNETIC BRAIDING AND QUASI-SEPARATRIX LAYERS
MAGNETIC BRAIDING AND QUASI-SEPARATRIX LAYERS
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DOI：
10.1088/0004-637x/704/2/1288
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发表时间：
2009-07
期刊：
影响因子：
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通讯作者：
A. Wilmot-Smith;G. Hornig;D. Pontin
中科院分区：
文献类型：
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作者：
A. Wilmot-Smith;G. Hornig;D. Pontin
挤压因子Q是磁场线映射的一个性质，它被认为是天体物理等离子体中电流片的形成以及随后的磁重联的一个指示器。在这里，我们对一类特殊的辫状磁场检验这一假设，这种磁场是日冕环的模型。我们探讨了准分离线层(QSL)之间的关系，即高Q值的层状结构、电流和积分平行电流之间的关系，后者是一个与重联率密切相关的量。研究发现，随着磁场编织程度的增加，Q值的最大值呈指数增加。同时，Q的分布变得越来越丝状，高Q层的宽度呈指数减小。随之而来的是层数的增加，因此，随着磁场的日益编织，体积变得被无数薄的准分子激光器占据。在这类辫状油田中，QSL并不能很好地预测当前特征。事实上，尽管存在多个QSL，但在理想弛豫下，与场相关的电流仍然是平滑的和大范围的；场动态调整到平滑平衡。与实际电流片相比，高Q值区域与高积分并联电流区的相关性更好。
The squashing factor Q, a property of the magnetic field line mapping, has been suggested as an indicator for the formation of current sheets, and subsequently magnetic reconnection, in astrophysical plasmas. Here, we test this hypothesis for a particular class of braided magnetic fields which serve as a model for solar coronal loops. We explore the relationship between quasi-separatrix layers (QSLs), that is, layer-like structures with high Q value, electric currents, and integrated parallel currents; the latter being a quantity closely related to the reconnection rate. It is found that as the degree of braiding of the magnetic field is increased, the maximum values of Q increase exponentially. At the same time, the distribution of Q becomes increasingly filamentary, with the width of the high-Q layers exponentially decreasing. This is accompanied by an increase in the number of layers so that as the field is increasingly braided the volume becomes occupied by a myriad of thin QSLs. QSLs are not found to be good predictors of current features in this class of braided fields. Indeed, despite the presence of multiple QSLs, the current associated with the field remains smooth and large scale under ideal relaxation; the field dynamically adjusts to a smooth equilibrium. Regions of high Q are found to be better related to regions of high integrated parallel current than to actual current sheets.