Influence of electron and ion diamagnetic drifts on kink modes in low-resistivity tokamak plasma

Abstract In the present paper, we numerically investigate the influence of electron and ion diamagnetic drifts on the nonlinear evolution of kink modes in low-resistivity plasma through the updated CLT code based on bi-fluid model. In the linear stage, electron or ion diamagnetic drift leads to a finite and constant mode rotation frequency. The mode frequency changes differently for cases dominated by electron or ion diamagnetic drift. For cases with dominating electron diamagnetic drift, the mode frequency significantly increases in the nonlinear stage; for cases with dominating ion diamagnetic drift, the mode frequency reduces to zero and even changes its sign. The sudden change of the mode frequency is due to the multiple-X-line reconnection process in low-resistivity plasma. During multiple-X-line reconnection, secondary islands merge into the 1/1 main island due to electron or ion diamagnetic drift, and the X-point of the 1/1 main island suddenly moves to another region. Then the local values of the electron or ion diamagnetic term change dramatically, leading to the sudden change of the mode frequency. In high-resistivity plasma, multiple-X-line reconnection does not occur, and the mode frequency will not change its sign. Meanwhile, if the mode rotates too fast, secondary islands will quickly merge into the 1/1 main island and will not develop to a large amplitude.