Formation and collapse of an internal transport barrier

A theoretical model of an internal transport barrier (ITB) is developed. Th e transport model based on the self-sustained turbulence theory of the curr ent diffusive ballooning mode is extended to include the effects of E x B r otation shear. Delayed formation of the ITB is observed in transport simula tions. The influence of finite gyroradius is also discussed. Simulation of the current ramp-up experiment successfully described the radial profile of density: temperature and safety factor. A model of ITB collapse due to mag netic braiding is proposed. Sudden enhancement of transport triggered by ov erlapping of magnetic islands terminates the ITB. The possibility of destab ilizing global low n modes is also discussed.