Magnetohydrodynamic simulation study of impurity radiation-excited and driven tearing mode

Tearing modes may play an important role in the density limit disruption. The Magnetohydrodynamic (MHD) code CLT with impurity modules is used to study the tearing mode excited and driven by impurity radiation. The impurity radiation can lead to plasma contraction and local enhancement of the current density. When the locally enhanced region of the current density approaches to the resonance surface, the tearing mode can be excited, even if the tearing mode is stable in the initial equilibrium. Through a scan of the initial atomic number (Z) and impurity concentrations, it is found that impurities with different Z values exhibit similar behaviors in the radiation-driven tearing mode. The impurity radiation can drive tearing mode growth through temperature cooling near the resonance surface, and there exists a linear relationship between the temperature perturbation caused by impurity radiation and the linear growth rate of the tearing mode. Additionally, the impurity can promote the growth of magnetic islands through the radiation cooling inside the magnetic island, and there exists a correlation between the initial parameters of impurity and the width of the saturated magnetic island.