PBX-M ohmic heating power supply upgrade

The ohmic heating (OH) power supply performs two functions in the PBX-M experiment. The OH system provides the voltage necessary for the initial discharge breakdown, and is the primary method of plasma current drive. In 1987 the PBX (Princeton Beta Experiment) device was upgraded to PBX-M (Princeton Beta Experiment-Modified). At that time, the OH power supply was reconfigured and portions of the control system were replaced. The upgrade provides control over the amount and duration of the voltage applied for initial discharge breakdown, more precise control of the overall current waveshape, and increases the total volt-seconds available for plasma current drive to 3 V-s. Details of the upgrade and operating experience from the previous run periods are presented along with discussions of the three leading candidate schemes for a proposed 1989-90 upgrade