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 have been studied in connection with E_r shear formation. The impro ved core confinement mode with ITB, the internal transport barrier, is roughly classified into "parabolic" type ITBs and "box" type ITBs. The parabolic type ITB has the reduced thermal diffusivity, X, in the core region; howevE_r, the E_r shear, dE_r/dr, is not so strong. The box type ITB has a very strong E_r shear at the thin ITB layer and the x value decreases to the level of neoclassical transport there. The estimated ExB shearing rate, ω_(E×B) becomes almost the same as the linear growth rate of the drift microinstability, γ_L, at the ITB layer in the box type ITB. Experiments of hot ion mode plasmas during the repetitive L-H-L transition shows that the thermal diffusivity clearly depends on the E_r shear and the strong E_r shear contributes to the reduced thermal diffusivity.