Applicability Verification of Tokamak Plasma Equilibrium Control Models

Abstract

The applicability of dynamic models used to evaluate the control performance of plasma equilibrium position is verfied through the use of data obtained in experiments with the HITACHI TOKAMAK HT-1. The major radius of the plasma in the HT-1 is 0.35 m. Emphasis has been placed on the evaluation of the bahavior of eddy currents on surrounding structures and on the evaluation of changes in the minor radius due to plasma displacement. An integral formulation of Maxwell equations has been solved numerically to evaluate eddy current behavior on the vacuum vessel and supporting disk. The calculated values obtained for the magnetic fileds generated by the eddy currents agree with the measured values obtained for those fields with an error of about 10 %. A comparison of the theoretical and measured values obtained for the sensitivity of plasma position to a step disturbance in the vertical coil power supply shows that the change that occurs in the minor radius of plasma because of plasma displacement is caused by the plasma's contact with the limiter. Feedback control gains of the HT-1 are adjusted on the basis of the results obtained from the models and phase margin criterion. The position of the plasma is regulated to within 5.0 mm of the desired position.