Programmable power supply for MST'S poloidal field

Abstract

We are designing a new programmable polo ida I 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 ofMST's inductive capabilities.The existing toroidal field programmable supply is based on series-parallel high-power IGBT "-bridges and has an output of about 40 MV A. The poloidal supply will also use high-power IGBTs and will provide about 120 MV A capability. The supply will drive the existing poloidal primary windings, connected with a 10:1 turns ratio. "-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.

Effects of oscillating poloidal current drive on magnetic relaxation in the Madison Symmetric Torus reversed-field pinch

“…applying OFCD, with dual PPSs. In addition to the toroidal magnetic field PPS used for the work reported in this paper, a new PPS for the poloidal field [36] was recently commissioned on MST, capable of producing a toroidal loop voltage oscillation and enabling OFCD with dual PPSs. This new PPS OFCD capability is much more flexible than the already-existing OFCD tank-circuit system [48], since, within PPS bandwidth limitations, essentially arbitrary oscillating waveforms are possible, and in particular, those with easily adjustable frequencies, as presented for OPCD in this paper.…”

“…In either case, the standard toroidal induction to sustain the RFP is supplied by a pulse-forming network in MST's poloidal magnetic field circuit. A programmable power supply (PPS) [36] in MST's toroidal magnetic field circuit provides poloidal current in the shell, which serves as the toroidal field coil, and this helps maintain standard field reversal as well as the oscillating loop voltage in OPCD cases. Apart from modulations and slow secular changes due to OPCD in those cases, plasma current I p is maintained at about 250kA.…”

Generation and suppression of runaway electrons in MST tokamak plasmas

“…A programmable power supply (PPS) is used to produce the toroidal magnetic field ('BT') [29]. This BT-PPS is comprised of 32 H-bridge modules using high-power insulatedgate bipolar transistors.…”

Simultaneous feedback control of toroidal magnetic field and plasma current on MST using advanced programmable power supplies

“…The volume-average beta is β = 2 − 5%, with electron and ion temperatures, T e,i 3 keV. For the work in this paper, low-current plasmas were studied using programmable switching power supplies [22,23] attached to the poloidal field transformer and toroidal magnet. Switching power supplies capable of larger current are under construction.…”

“…The analog output voltages are fed to one or both of the two programmable power supplies B t -PPS and B p -PPS. These supplies are IGBT-based switching supplies with bipolar outputs and a switching frequency of 10kHZ [22,23]. Each supply is powered by its own capacitor bank.…”