Energy confinement scaling for reversed-shear plasmas with internal transport barrier in JT-60U

An energy confinement scaling for reversed-shear plasmas with box-type internal transport barrier (ITB) and L-mode edge is developed based on the JT-60U data. The stored energy is divided into two parts: L-mode base part and core part surrounded by the ITB. The core stored energy W core does not simply increase with the net heating power P net . A scaling of core stored energy is given as W scale = Ce -1 f 1 B 2 p . f V core , where e f is the inverse aspect ratio at the ITB foot, B p,f is the poloidal magnetic field at the outer midplane ITB foot, and V core is the core volume inside the ITB foot. This scaling is equivalent to the condition for the core poloidal beta e f β p,core = C 1 with C 1 1 Though W core is little dependent on P net , the estimated heat diffusivity in the ITB region moderately correlates with a neoclassical diffusivity, and the neoclassical transport is not inconsistent with the data. The physics background of the present scaling is discussed.