Role of thermal conduction on resistive tearing mode in Tokamaks

We investigate the role of thermal conductivity on the evolution and saturation of the m/n = 2/1 resistive tearing mode (m and n are, respectively, the poloidal and toroidal Fourier mode numbers), by using a 3D toroidal MHD code (CLT). It is found that thermal conductivity has great influence on pressure and current profiles, and further affects the dynamic evolution of the tearing mode. Our simulation results indicate that the linear growth rate of the tearing mode increases, but the saturation level of magnetic islands decreases with increase of thermal conductivity. With a small thermal conductivity, a flattened distribution of the thermal pressure inside magnetic islands leads to a large pressure gradient at the edge that drives a ballooning mode to be unstable. We further found that the radial electric field at the magnetic island boundary and the vortex-like flow inside the magnetic island lead to a poloidally asymmetric transport barrier and reduce the thermal conductivity at the magnetic island boundary, which contributes to formation of an internal transport barrier.