This article summarizes the basics of power supply systems for magnets, especially the basic theory of AC/DC power converter systems for superconducting magnets. In order to control both excitation and demagnetization of the magnet, the power converter requires alternative DC voltage control capability. Since the current path from the converter system to the magnet is constant, the switching device requires reverse blocking capability to withstand reverse voltage. Thyristor converters are widely used as power converter systems for fusion magnets and accelerator magnets. The thyristor converter enables both excitation and demagnetization of the magnet by controlling the firing angle. The voltage source converter becomes a feasible option for magnet power supply systems. However, since the direction of DC voltage is constant, the power supply system requires a DC chopper in order to control the applied voltage of the magnet in both directions. The power flow between the threephase AC system and a voltage source converter is fundamentally determined by the voltage phase difference between the AC system and the converter.

The Large Helical Device (LHD) is a fusion plasma experimental device operating at the National Institute for Fusion Science. The LHD uses superconducting coils to generate a magnetic field for plasma confinement, and each coil is excited by a large-scale DC power supply. This paper introduces the DC power system and its design concept.

The superconducting Satellite Tokamak machine, “JT-60SA,” under construction at the National Institutes for Quantum and Radiological Science and Technology (QST) is an international collaborative project between Japan and Europe. It consists of superconducting toroidal and poloidal field coils, and some normal conductive in-vessel coils. This commentary describes the key features of the overall circuit configuration and the expected performance of each component of the power supply system for the superconducting magnets in JT-60SA.

The Japan Proton Accelerator Research Complex (J-PARC) began operations in 2008. The main ring (MR) of the J-PARC provides proton beams to two facilities: one is for the neutrino beam line, and the other is for the hadron experimental hall. A MR beam power of 470 kW has been achieved on the neutrino beam line. For high-power beam production, magnet power supplies require high accuracy for the output current to follow instructed current values. In order to improve the accuracy, we modified the magnet power supplies and electrical wiring between the power supply and magnets. Symmetrical wiring is essential to improve electric current tracking and reduce current ripples.

KEKB was the leading electron-positron collider in the world. Operation ceased in June 2010 in preparation for beginning the upgrade to SuperKEKB, the aim of which was to obtain a luminosity 40 times higher. For the SuperKEKB, over 2,000 magnet power supplies were recycled and approximately 300 power supplies were newly fabricated. The newly fabricated power supplies include high-performance power supplies: main bending/wiggler magnet power supplies and power supplies for final-focus superconducting magnets installed around the interaction point. High-power tests were performed and the results are reported.