Improved Confinement and Neoclassical Effect.

Abstract

Matrix Inversion (MI) method is developed in order to estimate the neoclassical ion thermal diffusivity, χNC, correctly. In the MI method, effects of impurity on χNC are treated self-consistently and no approximation on the friction and the viscosity matrix elements is carried out. The comparison of χNC value between the MI method and the Chang-Hinton’s (CH) formula shows that the CH formula over-estimates χNC value twice as large as that of MI method for typical JT-60U plasmas. The different dependence of χNC on the inverse aspect ratio, e, the effective charge number, Zeff, and the normalized ion collisionality, ν*i, between the MI method and the CH formula is presented. The radial electric field. Er, is estimated from the momentum and the heat momentum balance equations parallel to the magnetic field. Profiles of Er are compared between the two types of improved core confinement plasmas with internal transport barrier (ITB) in JT-60U, the “parabolic type ITB” and the “box type ITB”. In the box type ITB, the experimentally estimated thermal diffusivity. χexp, decreases in the core region. However, the Er shear is not so strong. In the box type ITB, a strong Er shear appears inside the ITB layer and the χexp value decreases drastically to the level of χNC. The E×B shearing rate becomes almost the same as the linear growth rate of the drift microinstability inside the ITB layer of the box type ITB.