Reconnection at multiply-connected null points

点击翻译按钮获取中文摘要

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.