Feedback Controller Synthesis for Tokamak Plasma Position Control

Abstract

A procedure for plasma controller synthesis using a system identification technique is proposed and is applied to position control in the HT-1 (Hitachi Tokamak) plasma. A linear dynamic model of the plasma position and the vertical field coil current is obtained from experimental data using the least-squares estimation method. The PI control gains are optimized on the basis of phase margin criterion using the frequency response of the model, and the plasma position can be regulated within a 5 mm deviation. The response sensitivity and its time constant derived from the model agree with values derived theoretically from the circuit equation assuming that the change in the plasma minor radius for a given plasma displacement is subject to plasma limiter interaction.