Reconnection at multiply-connected null points

全球磁场模型表明，太阳大气层中的零以各种复杂的方式配置。除了在一个理想化的连接两个零值的单一分离器处，我们对这里发生的重连知之甚少。本研究的目的是通过研究多连通零点系统的最简单例子，来更好地理解三维零点处的重联。该系统由两个零值（极性相反）组成，由两个分隔符连接。这项工作将开始，推导出双分离器的势场，然后通过向磁场中添加非势分量来平滑地引入电流。这个新的领域将形成的基础上进行数值松弛实验，使用Lare3d代码来解决理想的MHD方程，从该初始条件的重联实验将被收集。随后将通过运行相同的代码来研究重连，但是打开异常电阻率，使得电阻MHD方程将在电流超过临界值的网格点处求解。将研究本实验期间的能量变化（以及伴随的加热项），并与单个分离器情况下的能量变化进行比较。我们还将密切关注重联率和从扩散区释放的波（和等离子体流）的行为。该研究将解决的关键问题之一是，由于相邻扩散区域之间的场线的递归重连，多重连接零点中的重连率是否更高。

Global magnetic field models have shown that nulls in the solar atmosphere are configured in a variety of complex ways. Little is known about the reconnection that takes place here, except at an idealised single separator connecting two nulls. This research aims to better understand reconnection at 3d null points by studying the simplest example of a system of multiply-connected nulls. This system consists of two nulls (with opposite polarity) connected by two separators. The work will begin by deriving the double separator potential field before smoothly introducing a current by the addition of a non-potential component to the magnetic field. This new field will form the basis for a numerical relaxation experiment performed using the Lare3d code to solve the ideal MHD equations, from which the initial condition for the reconnection experiment will be gathered. The reconnection will subsequently be studied by running the same code but with an anomalous resistivity switched on, such that the resistive MHD equations will be solved at grid points whose current exceeds a critical value. The energy changes during this experiment (and accompanying heating terms) will be studied and compared with those found in the single separator case. We will also pay close attention to the reconnection rate and the behaviour of the waves (and plasma flows) released from the diffusion region. One of the key questions the research will address is whether the reconnection rate in multiply-connected null points is higher due to recursive reconnection of fieldlines between the neighbouring diffusion regions.