Effect of power deposition and current evolution on the formation of internal transport barriers

A model for internal transport barrier formation in tokamak plasmas [Newman et al., Phys. Plasmas 5 (1998) 938] is extended to include the evolution equation of the plasma current and a model of neutral beam injection power/particle deposition. The envelope density fluctuation level is evolved in time and coupled, via the E ×B shearing rate, to the ASTRA system of transport equations. As a practical realization of the model, reversed shear configurations in the TFTR tokamak are studied. It is found that, aside from the total input power, the detailed profiles of power deposition and current density play an essential role in the determination of the value of the transition power threshold.