Electrothermal dynamics of cold front in impure tokamak plasmas

Current density perturbations induced by radiative collapse, which is a possible mechanism governing tokamak plasma disruptions, have been investigated using a reaction–diffusion model. The reaction term of the current diffusion equation, which depends on the first and second radial derivatives of the electrical resistivity profile, produces a strong disturbance in the current density profile in a narrow layer of the cold front. While the current density locally increases in the region where the electron temperature gradient is steep, it decreases behind the cold front in the region where the electron temperature profile exhibits a pronounced concave-down curvature. The electrothermal dynamics driven by such a shape of the current density perturbation and the competition between Ohmic heating and impurity radiation are simulated by the tokamak transport code INDEX.