Stability of double tearing mode in current hole configuration

Tsuda, Takashi; Kurita, Genichi; Fujita, Takaaki

The current density is expected to be negative in the central region of the tokamak when the amplitude of bootstrap current or off-axis current drive is large enough. However, a flat current profile with almost zero value has been observed in experiments even under the situation with negative one-turn voltage exists in the central region of plasma. Double tearing mode (DTM) can be unstable for the current profile with a "current hole" and some MHD activities are observed in JET before the formation of the current hole. On the contrary, no MHD activity is observed in the JT-60 experiment. Here, we study the condition of appearance of DTM and investigate the stability of DTM and the interaction between DTM (n=1 perturbation) and "Current Hole" with resistive RMHD simulations.