Control of a superconducting coil by a MOSFET power converter operating at near liquid nitrogen temperature

The on-resistance of a power MOSFET has a minimum value at around 80 K. This characteristic was utilized in order to operate a power converter circuit using power MOSFETs in a cryostat with a superconducting coil. As a result, it was confirmed that power losses of the chopper circuit and the size of the current leads can be greatly reduced. The power loss of the circuit was half of that at room temperature, and the loss can be reduced further by using diodes with lower on-voltages at low temperatures. The size of the current leads was reduced by using the chopper circuit as a DC transformer.