Role of Hall effect on the resistive kink mode in tokamaks

Abstract

The influence of the Hall effect on the nonlinear evolution of the m/n=1/1 resistive-kink mode is numerically investigated by the three-dimensional toroidal Hall-MHD code CLT. It is found that the Hall effect can lead to the explosive growth of the resistive-kink mode at the nonlinear stage. The explosive nonlinear growth of the resistive-kink mode mainly results from the structural transition of the current sheet in the Hall-MHD simulations. At the nonlinear stage, the geometry of the current sheet turns into X-type from Y-type, resulting in the significant acceleration of the reconnection process. The fast reconnection induced by the Hall effect may explain the fast crash observed in large Tokamaks. We also found that there exists a critical value of the ion inertial length d_i that is resulted from the acceleration of magnetic reconnection due to the decoupling motions of ions and electrons and the suppression effect by the electron diamagnetic rotation in the Hall MHD. The critical value of d_i decreases with increasing thermal conductivity Κ_⊥ . When d_i exceeds a critical value, the peak growth rate decreases with increasing Κ_⊥ .