Reduced transport and E_r shearing in improved confinement regimes in JT-60U

摘要

The global confinement and the local transport properties of improved core confinement plasmas in JT-60U were studied in connection with E. shear formation. In the improved core confine- ment mode with internal transport barriers (ITBs), these are roughly classified into ‘parabolic type' ITBs and ‘box type' ITBs. The parabolic type ITB has a reduced thermal diffusivity X in the core region; however, the E_r shear, dE_r/dr, is not as strong. The box type ITB has a very strong E_r shear at the thin ITB layer and X decreases to the level of neoclassical transport there. The estimated E × B shearing rate, ωE×B, becomes almost the same as the linear growth rate of the drift microinstability, γL, at the ITB layer in the box type ITB. Experiments with hot ion mode plasmas during the repet- itive L-H-L transition showed that the thermal diffusivity clearly depends on the E_r shear and the strong E_r shear contributes to the reduced thermal diffusivity.