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

Programmable control of the inductive electric field enables advanced operations of reversed-field pinch (RFP) plasmas in the MST device and further develops the technical basis for ohmically heated fusion RFP plasmas. MST's poloidal and toroidal magnetic fields ($B_\text{p}$ and $B_\text{t}$) can be sourced by IGBT-based programmable power supplies (PPSs). In order to provide real-time simultaneous control of both $B_\text{p}$ and $B_\text{t}$ circuits, a time-independent integrated model is developed. The actuators considered for the control are the $B_\text{p}$ and $B_\text{t}$ primary currents produced by the PPSs. The control system goal will be tracking two particular demand quantities: the plasma current $I_\text{p}$, directly related to $B_\text{p}$, and the RFP reversal parameter $F$, closely related to $B_\text{t}$. To understand the responses of $I_\text{p}$ and $F$ to the actuators and to enable systematic design of control algorithms, dedicated experiments are run in which the actuators are modulated, and a linearized dynamic data-driven model is generated using a system identification method. We perform a series of initial real-time experiments to test the designed feedback controllers and validate the derived model predictions. The feedback controllers show systematic improvements over simpler feedforward controllers.