以HarrisSheet作为初始条件，使用数值模拟的方法，研究了二级磁岛不稳定重联的一些性质．在模拟中随着初始扰动的加入，HarrisSheet将演化到非线性阶段，形成更薄的有剪切速度的电流片，并伴有一级磁岛产生．当Lundquist数大于或等于10^5时，非均匀剪切速度的Sweet-Parker电流片开始不稳定，并有二级磁岛出现．不稳定Sweet—Parker电流片对应的临界长宽比为65．Lundquist数越大，演化形成的Sweet—Parker电流片越薄，更多的二级磁岛将出现，且沿电流片两边向外喷出%In this paper, numerical simulation results of nonlinear Plasmoid instabilities are presented. A two dimensional incompressible MHD code is used to calculate the results. The adaptive mesh refinement and MPI techniques are enable in this code. Harris sheets are used as the initial equilibrium conditions and small perturbations of the current density are applied to make the system unstable. Sequences of plasmoid instability processses for different Lundquist numbers have been studied. The Harris sheets will always evolve in to thinner Sweet-Parker current sheets with shearing flows in the early stage. As the Lundquist number S 〉/10^5, the Sweet-Parker thin current sheets are unstable and secondary islands appear. The critical aspect ratio for the unstable Sweet-Parker thin current sheet is around 65. The larger the Lundquist number is, the thinner the Sweet-Parker sheet, and the more secondary islands appear. These secondary islands are ejected out along the current sheet, grow bigger with time and coalesce with each other in the later stage. The reconnection rate of the current sheet has been increased a lot due to secondary instabilities. The peak reeonnection rates in each reconneetion processes for different Lundquist number are picked about to study the relationship between the Lundquist number and the reconnection rate, which has been found no longer scales with Lundqnist number as S-2/1, but weakly depends on S.
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