Formation and collapse of an internal transport barrier

A theoretical model of an internal transport barrier (ITB) is developed. The transport model based on the self-sustained turbulence theory of the current diffusive ballooning mode is extended to include the effects of E ×B rotation shear. Delayed formation of the ITB is observed in transport simulations. 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 magnetic braiding is proposed. Sudden enhancement of transport triggered by overlapping of magnetic islands terminates the ITB. The possibility of destabilizing global low n modes is also discussed.