Power supplies for poloidal magnets in the Alcator C-MOD tokamak

The highly flexible plasma shaping and diverter configuration of Alcator C-MOD necessitates the use of many separate magnet power supply systems. Eleven separate systems are used to power the 14 magnets in the tokamak. The severe budgetary constraints prevented the purchase of an entirely new converter set for each of these 11 systems. The solution to this dilemma was the long-term loan of the TMX Upgrade magnet power supplies from Lawrence Livermore National Laboratory to MIT. The converters operate in groups of two or three to power four of the 10 poloidal field magnet systems and to provide excitation to the alternator. The `TMX supplies´ have been completely overhauled and redesigned for their use in the Alcator program. All have new control logic, PLC interface, and gate drive circuits. Several have been modified to provide two-quadrant operation. The AC and DC bus has been redesigned and simplified. Twelve of the units are mounted in a double-high rack to preserve floor space. The AC unit substations are located near the converters to minimize resistive and reactive losses. Some test data from rebuilt supplies are presented along with details of the interface to the Alcator control system. All power supplies have been pulse tested to 300 V at 5 kA into an inductive load