Radiation-driven islands of the resistive tearing mode in Tokamaks*

We investigate the influence of the bremsstrahlung radiation 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). Being the power balance between the Ohmic heating and the radiative cooling inside the magnetic island, the stability criterion for radiation driven islands has been taken into account. It is found that if impurities (such as carbon, iron and tungsten, etc.) exist in the magnetic island, strong destabilization of the tearing mode will be made due to an imbalance of local radiative cooling and Ohmic heating inside the island. As a result, the width of the magnetic island will increase significantly, even larger than twenty percent of the minor radius. Moreover, the radiation reduces the pressure inside the magnetic island and further shrinks the current profile inside the island. The modified Rutherford equation (MRE), which contains radiation and current asymmetric effects, can reasonably explain the above physical mechanism of radiation-driven magnetic island growth.