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arXiv 1003.5784astro-ph.SRphysics.plasm-ph
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编织日冕环II的动力学:级联到多个小尺度重联事件

Dynamics of braided coronal loops II: Cascade to multiple small-scale reconnection events

D. I. Pontin, A. L. Wilmot-Smith, G. Hornig, K. Galsgaard

摘要:

目的:我们的目的是研究含有编织磁通量但没有净电流或螺旋度的磁环的电阻弛豫。该回路受系线边界条件的约束。我们调查的动力学过程中发生的放松,特别是磁重联发生,并讨论最终平衡的性质。方法:编织磁场的三维演变是遵循一系列的电阻MHD模拟。结果:研究发现,随着环内的不稳定性,无数的薄电流层形成,通过级联状的过程。这种叶栅变得更加发达,并持续更长的时间为更高的磁雷诺数。在级联过程中,磁通量被重联多次,这种“多重重联”的水平与磁雷诺数呈正相关。最终,系统演化到不再有小规模电流层的状态。这个最终状态被发现近似于一个非线性的无力场,由两个相反的符号扭曲的磁通管嵌入在一个均匀的背景场。

英文摘要:

Aims: Our aim is to investigate the resistive relaxation of a magnetic loop that contains braided magnetic flux but no net current or helicity. The loop is subject to line-tied boundary conditions. We investigate the dynamical processes that occur during this relaxation, in particular the magnetic reconnection that occurs, and discuss the nature of the final equilibrium. Methods: The three-dimensional evolution of a braided magnetic field is followed in a series of resistive MHD simulations. Results: It is found that, following an instability within the loop, a myriad of thin current layers forms, via a cascade-like process. This cascade becomes more developed and continues for a longer period of time for higher magnetic Reynolds number. During the cascade, magnetic flux is reconnected multiple times, with the level of this `multiple reconnection' positively correlated with the magnetic Reynolds number. Eventually the system evolves into a state with no more small-scale current layers. This final state is found to approximate a non-linear force-free field consisting of two flux tubes of oppositely-signed twist embedded in a uniform background field.

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