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 Wcore does not simply increase with the net heating power Pnet. A scaling of core stored energy is given as Wscale = Cεf-1Bp,f2Vcore, where εfis the inverse aspect ratio at the ITB foot, Bp,f is the poloidal magnetic field at the outer midplane ITB foot, and Vcore is the core volume inside the ITB foot. This scaling is equivalent to the condition for the core poloidal beta εfβp,core = C1 with C1≈¼. Though Wcore is little dependent on Pnet, 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.