Numerical Studies of Fast Pressure Crash Associated with Double Tearing Modes

The fast pressure crash associated with the nonlinear evolution of DTMs is investigated using a three-dimensional toroidal and nonlinear MHD code CLT. Our simulation results indicate that the fast pressure crash is not directly related to the explosive growth of DTM because the explosive growth of the DTM takes place in the earlier nonlinear phase and the fast pressure crash happens in the much later nonlinear stage. It is also found that the explosive growth lasts much longer than the fast pressure crash. At almost the end of the explosive growth phase, the magnetic fields around the magnetic axis become stochastic, and a strong radial flow is generated. The radial flow can effectively transfer the hot plasma around the magnetic axis into the outer cold region and consequently leads to the fast crash of the pressure in the core. As a result, the dependence of the crash time on the resistivity is very weak. It is also found that the geometry of Tokamaks has very weak influence on the fast pressure crash.