Multiple secondary islands formation in nonlinear evolution of double tearing mode simulations

A new numerical code solving the conservative perturbed resistive magnetohydrodynamic (MHD) model is developed. Numerical tests of the ideal Kelvin-Helmholtz instability and the resistive double tearing mode (DTM) show its capability in solving linear and nonlinear MHD instabilities. The nonlinear DTM evolution in 2D geometry is numerically investigated with low guiding field Bz0, short half-distance y(0) between the equilibrium current sheets, and small resistivity g. The interaction of islands on the two initial current sheets may generate an unstable flow driven current sheet with a high length-to-thickness aspect ratio (a), and multiple secondary islands can form. In general, the length-to-thickness aspect ratio a and the number of secondary islands increase with decreasing guide field B-z0, decreasing half-distance y(0), and increasing Lundquist number of the flow driven current sheet SL although the dependence may be non-monotonic. The reconnection rate dependence on SL, B-z0, and y(0) is also investigated. Published by AIP Publishing.