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

Abstract

Abstract Programmable control of the inductive electric field enables advanced operations of reversed-field pinch (RFP) plasmas in the Madison Symmetric Torus (MST) device and further develops the technical basis for ohmically heated fusion RFP plasmas. MST’s poloidal and toroidal magnetic fields (B p and B t) can be sourced by programmable power supplies (PPSs) based on integrated-gate bipolar transistors (IGBT). In order to provide real-time simultaneous control of both B p and B t circuits, a time-independent integrated model is developed. The actuators considered for the control are the B p and B t primary currents produced by the PPSs. The control system goal will be tracking two particular demand quantities that can be measured at the plasma surface (r = a): the plasma current, I p ∼ B p(a), and the RFP reversal parameter, F ∼ B t(a)/Φ, where Φ is the toroidal flux in the plasma. The edge safety factor, q(a) ∝ B t (a), tends to track F but not identically. To understand the responses of I 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.