Nonlinear evolution of double tearing mode with guiding magnetic field

Nonlinear dynamic evolution of the double tearing mode (DTM) with a guiding magnetic field (B-y0) is investigated by magnetohydrodynamical numerical simulation. The dynamic process of DTM depends weakly on the guiding field in the weak guiding field regime (B-y0 <= 1), but is suppressed by a strong guiding field (B-y0 > 2). During the explosive nonlinear phase, the maximum reconnection rate (gamma(max)) increases weakly with the increase of the resistivity as gamma(max) eta(0.06) for B-y0 <= 1, but for B-y0 > 2, gamma(max) is nearly independent of the resistivity. The maximum reconnection rate in the explosive growth phase increases with increase of the initial current sheet separation. A secondary tearing instability is observed at moderate current sheet separation. A strong guiding field suppresses the formation of a secondary island. Based on the simulation results, it is found that the secondary tearing instability occurs only when the length-to-thickness aspect ratio of the reconnection region exceeds about 20. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3581064]