二维和三维湍流磁重联
Turbulent magnetic reconnection in 2D and 3D
摘要：
磁场嵌入在一个完美的导电流体保持其拓扑结构的所有时间。虽然电离的天体物理物体，如恒星和星系盘，几乎是完全导电的，但它们在动态时间尺度上显示出拓扑变化的迹象，即“磁重联”。重联可以直接在日冕中观察到，但也可以从恒星内部存在的大规模发电机活动中推断出来。太阳耀斑和伽玛射线暴通常与磁重联有关。以前的工作集中在展示如何在碰撞率非常小的等离子体中快速重连。在这里，我们提出了数值证据，三维模拟的基础上，在湍流流体中的重连发生在一个速度相当于湍流的均方根速度，无论电阻率的值。特别是，对于比磁场压力弱得多的湍流压力，这是正确的，使得磁场线仅被湍流稍微弯曲。这些结果与Lazarian和Vishniac（1999）的提议一致，即重联是由磁场线的随机扩散控制的，它产生了从重联区流出的广泛的等离子体。这项工作意味着湍流流体中的重联通常发生在大约一个单一的涡流周转时间，对整个宇宙的发电机活动和粒子加速具有广泛的影响。相比之下，在湍流的存在下，在2D配置中的重连取决于电阻率，即是缓慢的。
英文摘要：
Magnetic field embedded in a perfectly conducting fluid preserves its topology for all time. Although ionized astrophysical objects, like stars and galactic disks, are almost perfectly conducting, they show indications of changes in topology, `magnetic reconnection', on dynamical time scales. Reconnection can be observed directly in the solar corona, but can also be inferred from the existence of large scale dynamo activity inside stellar interiors. Solar flares and gamma ray busts are usually associated with magnetic reconnection. Previous work has concentrated on showing how reconnection can be rapid in plasmas with very small collision rates. Here we present numerical evidence, based on three dimensional simulations, that reconnection in a turbulent fluid occurs at a speed comparable to the rms velocity of the turbulence, regardless of the value of the resistivity. In particular, this is true for turbulent pressures much weaker than the magnetic field pressure so that the magnetic field lines are only slightly bent by the turbulence. These results are consistent with the proposal by Lazarian and Vishniac (1999) that reconnection is controlled by the stochastic diffusion of magnetic field lines, which produces a broad outflow of plasma from the reconnection zone. This work implies that reconnection in a turbulent fluid typically takes place in approximately a single eddy turnover time, with broad implications for dynamo activity and particle acceleration throughout the universe. In contrast, the reconnection in 2D configurations in the presence of turbulence depends on resistivity, i.e. is slow.
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