Studies on impact of electron cyclotron wave injection on the internal transport barriers in JT-60U weak shear plasmas

Impact of the electron cyclotron range of frequency wave (ECRF) on the internal transport barriers (ITBs) in a weak shear (WS) plasma has been investigated in JT-60U. The fundamental O-mode ECRF of 110 GHz injected obliquely (co-current drive) from the low field side is used. It is observed that the ion temperature ( T i ) ITB in a WS plasma can be degraded by ECRF. It is clarified for the first time that the degradation depends increasingly on the EC power ( P EC ) but decreasingly on the plasma current ( I p ). Moreover it is confirmed that ECRF affects the toroidal rotation ( V t ) indirectly and results in the flattening of V t (ρ) and therefore the radial electric field ( E r ) profiles regardless of the direction of the target V t (ρ), peaking co or counter direction (relative to the I p direction). Furthermore, it is recently found that T i and V t in the whole ITB region are affected with almost no delay from the EC onset even with off-axis EC deposition. These results indicate that EC injection unveiled a semi-global structure that characterizes T i ITB in a WS plasma.