Operating characteristics of an energy transfer system between superconducting magnets with the chopper circuit

Heavy instantaneous electric power is necessary for energizing a large pulsed superconducting magnet, e.g. some thousands of MW of power will be required to operate a poloidal magnet system of tokamak-type fusion reactor. Since this kind of heavy demand will cause a disturbance to the commercial power system, a power supply as consisting of an energy storage unit and an energy transfer circuit must be developed for a practical application of pulsed superconducting magnets. One of the most favorable candidates for this purpose is the combination of a superconducting magnetic energy storage with a transfer circuit. Therefore, we developed an energy transfer system which consists of a 4MJ-class pulsed superconducting magnet, a 3MJ-class pulsed superconducting magnet and a chopper-type energy transfer circuit so as to prove the effectiveness of energy transfer between superconducting magnets and succeeded in MJ-class reversible bipolar energy transfer experiments between these magnets. The chopper-type circuit was adopted for such merits as low capacitance voltage, small current ripple and relatively low cost. With regard to the transfer efficiency, one of important subjects of a transfer system, high value of 93 % was achieved in 3MJ-class transfer. This value can be further improved by optimizing operating conditions. We also estimated circuit losses of the whole system and compared them with experimental results. Consequently, it was made clear that the system characteristics is described by an energy conserving equation taking account of circuit losses. (author)