Poloidal and Toroidal Programmable Power Supplies on MST*

For the first time, MST has been operated with two separate IGBT-based Programmable Power Supplies, giving precise, simultaneous control of MST's poloidal (BP) and toroidal (BT) fields via pre-programmed waveforms or real-time feedback control.

Based on system identification, advanced closed-loop controllers enable good waveform control for physics investigations of self-organization in RFPs and disruption-related phenomena in tokamaks.

Improved plasma formation over a wide range of currents allows realistic comparisons with numerical MHD simulation codes.

Several years' operation of the BT PPS has pointed the way to design improvements which are incorporated into the BP PPS. Improvements include seven-level Pulse Width Modulation, allowing more current to be drawn from each IGBT and reducing radiated noise; modular construction with isolated charging, control, and monitoring; and electronic capacitor dump system which eliminates relays and improves capacitor lifetime.

Upgrades to the BP PPS are underway which will increase the maximum plasma current from the present 96 kA to 480 kA.