Current drive operation in a tokamak

Three modes of current drive operation in a tokamak — continuous, cyclic, and rfinitiated-are studied for air core and iron core transformer. It is found that the air core transformer is in general more flexible than the iron core transformer for current drive operation. For continuous operation, the shutoff time of the Ohmic heating circuit of the air core transformer can be reduced to zero by using a bias current. On the other hand, the shutoff time of the iron core transformer remains finite even if the bias current is used, because of hysteresis. For cyclic operation, methods of shortening the recharging time are investigated for both types of transformer. The effects of the transformer on rf-initiated operation are investigated. A model design of a saturable iron core tokamak for current drive experiments is also presented.