High-speed, high-accuracy magnet power supply using FET chopper for synchrotron facility

The bending magnet power supply for the accelerator built at the NTT LSI Laboratories must be able to quickly control the current for highly inductive coils with very high accuracy during the transition from the rising slope to the flat top as well as the flat top of the current reference. To meet this requirement, a new power supply has been developed which consists of four DC power supplies, an inverter, a forcing, and two high-speed choppers. The high-speed chopper is made up of 200 MOSFETs connected in parallel that are switched at 33 kHz. The control circuit has a fast response with a crossover frequency of 4000 rad/s. Test results show that the deviation between the reference and the actual current is within ±1×10^-4, when the current through a magnet coil which has a time constant of 3.3 s is increased to the rated current of 800 A at the rate of change of 660 A/s