Modeling and Measurement of Eddy Currents in the ETE Spherical Tokamak

Abstract. A series of calculations and measurements have been made to evaluate the effect of eddy currents in the spherical tokamak ETE (Experimento Tokamak Esférico). Eddy currents occur in the central column of the conventional copper toroidal field magnet, around which the ohmic heating solenoid was tightly wound, and in the continuous wall of the vacuum vessel manufactured from inconel alloy. During the startup phase, the currents circulating in the central column strongly affect the performance of the ohmic heating system, while the currents flowing in the vacuum vessel introduce large error fields that must be compensated for successful plasma breakdown and must also be taken into account in the magnetic reconstruction procedure. Elaborate analytical models have been developed to represent both systems of currents. The results of these models are compared with experimental values of the ohmic solenoid impedance, with the operation of the ohmic heating system, and with the measured distribution of eddy currents in sections of the vacuum vessel.