The present generation of large tokamak experiments all make large electric power demands to supply their four main pulsed loads (toroidal field coils, poloidal field coils, poloidal field amplifiers and additional heating). These individual load requirements are described for three tokamaks, and the overall pulses are compared with the capabilities of their external bulk power supply systems. The technical and economic arguments for supplying the poloidal field coils from flywheel-generator-convertors are discussed. Typical poloidal field current and voltage requirements are described, and are seen to involve the removal of magnetic energy at very high power levels during one of the five phases of a tokamak's operation. This is conveniently achieved by using DC interrupters to divert the current into discharge resistors, and the techniques available for DC interruption are reviewed. The complete poloidal field power supply circuit is described, including its performance during each of the five phases. Seven fault conditions are identified and their impact on the design is discussed. The influence of the rectifier on the generator design and performance is examined, with particular reference to the harmonics. In concluding, mention is made of future commercial fusion reactors and their power supplies.
