Effects of resistivity and viscosity on dynamic evolution and radial position change of m/n = 3/1 double tearing mode

The effects of the plasma resistivity and viscosity on the dynamic evolution of the m/n = 3/1 double tearing mode (DTM) are studied and analyzed quantitatively using the CLT (Ci-Liu-Ti, which means magnetohydrodynamics in Chinese) code. In this work, we mainly focus on the change in the radial positions and the oscillatory dynamics of the magnetic islands grown on the two rational surfaces. We conduct a systematic investigation on the effect of viscosity on the DTM dynamics, which has rarely been studied before. From the results of the study, it is observed that the time required for entering the explosive phase decreases with decreasing viscosity. In the nonlinear phase, the kinetic energy exhibits an oscillatory behavior due to the magnetic flux injection and magnetic reconnection, and the oscillation amplitude is suppressed for a large viscosity due to dissipation. The effects of the plasma resistivity and viscosity on the change in the radial positions of magnetic islands are systematically explained. The change in the radial positions of magnetic islands occurs in an abrupt growth phase before the kinetic energy reaches its maximum value. Multiple position changes take place with a relatively higher reconnection rate and magnetic flux injection at low viscosity damping. A large range of radial vortices formed as a result of the change in the positions may have a positive effect on the transport.