Lower hybrid current drive in the presence of a DC electric field

A code for numerical modelling of lower hybrid current drive has been developed which takes into account the DC electric field. The model is based on the Fokker-Planck equation, the plasma circuit equation and the power balance equations. The flow of power supplied by the RF waves and the OH coil (transformer) is investigated. Also studied are the current drive efficiency and the ramp-up efficiency, which is the ratio of RF energy to plasma electromagnetic energy. The ramp-up rate of the plasma current is slower and the RF power required for recharging the OH coil is higher when the DC electric field is taken into account than when it is neglected. The simulation results agree well with the results of Alcator C experiments. The RF energy and the time for ramp-up and recharge required for the next-generation tokamak are estimated.

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