Programmable power supply for MST´S poloidal field

We are designing a new programmable poloidal field power supply for the MST reversed-field pinch. By providing flexible waveform control, the new supply will expand capabilities in oscillating field current drive, inductive current profile control, and other inductive techniques. The new power supply will allow use of the full flux swing of MST´s poloidal transformer core without a separate core bias supply and its isolating inductor. It will also eliminate the risk of harmful surge currents due to core saturation on unplanned termination of the plasma discharge. Used together with the newly-installed toroidal field programmable power supply, the new poloidal supply will allow maximum use of MST´s inductive capabilities. The existing toroidal field programmable supply is based on series-parallel high-power IGBT H-bridges and has an output of about 40 MVA. The poloidal supply will also use high-power IGBTs and will provide about 120 MVA capability. The supply will drive the existing poloidal primary windings, connected with a 10:1 turns ratio. H-bridges will be series-connected in groups of three to yield up to +/-2700 V output; these groups will then be connected in parallel to allow output currents up to +/-80 kA. The power supply units are modular, enabling future expansion for more output capability, and are based on low-inductance laminated heavy copper buses. Waveform generation will be controlled using seven-level Pulse Width Modulation, to reduce IGBT heating and minimize output distortion and noise generation. Overall control of the new poloidal supply will be via General Atomics´ Plasma Control System.