Center For Integrated Plasma Studies, Department of Physics, University of Colorado, Boulder, Colorado 80309, USA.
Nature. 2011 Jun 1;474(7350):184-7. doi: 10.1038/nature10091.
During magnetic reconnection, the field lines must break and reconnect to release the energy that drives solar and stellar flares and other explosive events in space and in the laboratory. Exactly how this happens has been unclear, because dissipation is needed to break magnetic field lines and classical collisions are typically weak. Ion-electron drag arising from turbulence, dubbed 'anomalous resistivity', and thermal momentum transport are two mechanisms that have been widely invoked. Measurements of enhanced turbulence near reconnection sites in space and in the laboratory support the anomalous resistivity idea but there has been no demonstration from measurements that this turbulence produces the necessary enhanced drag. Here we report computer simulations that show that neither of the two previously favoured mechanisms controls how magnetic field lines reconnect in the plasmas of greatest interest, those in which the magnetic field dominates the energy budget. Rather, we find that when the current layers that form during magnetic reconnection become too intense, they disintegrate and spread into a complex web of filaments that causes the rate of reconnection to increase abruptly. This filamentary web can be explored in the laboratory or in space with satellites that can measure the resulting electromagnetic turbulence.
在磁重联过程中，磁场线必须断开并重新连接，以释放驱动太阳和恒星耀斑以及太空中和实验室中其他爆炸事件的能量。这究竟是如何发生的还不清楚，因为需要耗散来破坏磁场线，而经典碰撞通常很弱。由湍流引起的离子-电子拖拽，被称为“反常电阻率”，以及热动量输运是两种被广泛引用的机制。在空间和实验室中磁重联点附近的增强湍流的测量支持反常电阻率的想法，但还没有测量表明这种湍流产生了必要的增强拖拽。在这里，我们报告的计算机模拟表明，在最感兴趣的等离子体中，即磁场主导能量预算的等离子体中，两种以前被看好的机制都不能控制磁场线如何重新连接。相反，我们发现，当在磁重联过程中形成的电流层变得过于强烈时，它们会分解并扩散成复杂的细丝网络，导致重联速度突然增加。这种丝状网络可以在实验室或空间中通过可以测量产生的电磁湍流的卫星来探索。
