Uzdensky D A, Loureiro N F
Center for Integrated Plasma Studies, Physics Department, UCB-390, University of Colorado, Boulder, Colorado 80309, USA.
Instituto de Plasmas e Fusão Nuclear, Instituto Superior Técnico, Universidade de Lisboa, 1049-001 Lisboa, Portugal.
Phys Rev Lett. 2016 Mar 11;116(10):105003. doi: 10.1103/PhysRevLett.116.105003. Epub 2016 Mar 9.
The recent realization that Sweet-Parker current sheets are violently unstable to the secondary tearing (plasmoid) instability implies that such current sheets cannot occur in real systems. This suggests that, in order to understand the onset of magnetic reconnection, one needs to consider the growth of the tearing instability in a current layer as it is being formed. Such an analysis is performed here in the context of nonlinear resistive magnetohydrodynamics for a generic time-dependent equilibrium representing a gradually forming current sheet. It is shown that two onset regimes, single-island and multi-island, are possible, depending on the rate of current sheet formation. A simple model is used to compute the criterion for transition between these two regimes, as well as the reconnection onset time and the current sheet parameters at that moment. For typical solar corona parameters, this model yields results consistent with observations.
最近认识到，斯威特-帕克电流片对二次撕裂（等离子体团）不稳定性极其不稳定，这意味着这种电流片在实际系统中不可能出现。这表明，为了理解磁重联的起始，人们需要考虑电流层在形成过程中撕裂不稳定性的增长。本文在非线性电阻磁流体动力学的背景下，针对一个代表逐渐形成的电流片的一般随时间变化的平衡态进行了这样的分析。结果表明，根据电流片的形成速率，可能存在两种起始状态，即单岛状态和多岛状态。一个简单模型被用来计算这两种状态之间转变的判据，以及重联起始时间和此时的电流片参数。对于典型的日冕参数，该模型得出的结果与观测结果一致。
