Stabilization of Neoclassical Tearing Mode by Electron Cyclotron Wave Injection in JT-60U

Abstract

Real‐time neoclassical tearing mode (NTM) stabilization system has been developed in JT‐60U. In this system, mode location is first identified by calculating the plasma shape using the Cauchy condition surface method and evaluating electron temperature perturbation profile in real time. Subsequently, steerable mirror angle is changed so that electron cyclotron (EC) wave is absorbed at the mode location. By using this system, a 3/2 NTM has been completely stabilized, and an increase in the beta value and H‐factor has been observed after the stabilization. Effects of EC injection before the NTM onset (‘early EC injection’) have been investigated. It is found that the NTM is more strongly suppressed for the early injection compared with the case of EC injection after the saturation of the NTM growth (‘late EC injection’). It is also found that the suppression effect for the early injection strongly depends on the EC injection angle, as in the case of the late EC injection.