Simulations on impurity radiation induced tearing mode growth during massive gas injection in tokamaks*

The impurity radiation induced tearing mode growth during massive gas injection is studied in simulations using the 3D resistive MHD model implemented in the NIMROD code. Two scenarios are identified, namely, the island growth caused by the global current profile contraction as a result of impurity penetration from the plasma edge into the central region, and the tearing mode growth triggered by the local impurity radiation cooling due to the local impurity deposition on the rational surface through the reversal of the Glasser, Greene, and Johnson (GGJ) stabilization effect. After the magnetic island formation, the radiation-induced magnetic islands rotate with the poloidal flow that is mainly driven by the electromagnetic torque from the local redistribution of current density induced by impurity penetration and radiation.