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Extra-Low-Voltage DC Power Supply for Large-Scale Superconducting Coil for Fusion Device

A helical-type fusion reactor uses huge-scale dc superconducting magnets driven up to 100-kA dc to make a steady-state magnetic field to confine the fusion plasma. The required voltage to keep the current in the steady-state operation is close to zero; thus, a dc power supply is required, whose output rating is 100 kA and 0.1 V. To realize such low-voltage power supply, a converter that works under low frequency such as 0.1 Hz is applicable due to the large load inductance. Having such a low-frequency-and-voltage operation, mechanical contacts driven by piezo devices can be beneficially used as switching devices in the converter. With this switching device, the forward voltage drop becomes lower than the semiconductor devices, and the power loss in the steady state can be reduced. A conceptual design of this converter has been made confirming the operation of a piezo-driven mechanical switch device in dc power supply.