Control of radiation-driven tearing mode by externally driven current in tokamaks

The radiation-driven tearing mode (RTM) in tokamaks was numerically studied in our previous investigation (Xu et al 2020 Plasma Phys. Control. Fusion 62 105009), and it was noticed that radiation cooling could drive magnetic island growth and could even cause disruption due to the nonlinear mode coupling. In this work, the suppression of the radiation-driven m/n = 2/1 tearing mode by an externally driven current is investigated numerically by using a three-dimensional toroidal code CLT (Ci-Liu-Ti means magnetohydrodynamics in Chinese) based on a full set of resistive magnetohydrodynamic equations. It is found that an externally driven current with appropriate turn-on time and strength can effectively stabilize the RTM. The effects of the asymmetry current and multi-mode coupling can be stabilized effectively by the externally driven current. In the nonlinear stage, under the influence of the radiation, a strong m/n = 1/0 mode is generated due to the hot-core shift caused by the decrease of the core thermal pressure, which is irreversible even if the m/n = 2/1 magnetic island could be effectively controlled by the externally driven current. When the externally driven current is turned on in the linear stage, it very efficiently and quickly suppresses the dominant modes, and the hot-core shift effect also becomes weaker because of the smaller m/n = 1/0 mode. Moreover, it is found that external auxiliary heating with appropriate intensity in the core region can effectively balance the reduced pressure and can further control the hot-core shift caused by radiative cooling.