APPROXIMATION OF EDDY CURRENTS IN 3-DIMENSIONAL STRUCTURES BY TOROIDALLY SYMMETRICAL MODELS, AND PLASMA CONTROL ISSUES

The eddy currents induced in three dimensional structures of in-vessel components in tokamaks and their influence on the plasma controls are investigated. The in-vessel components in ITER are used as an example . A simple method of modifying a toroidally symmetric two dimensional (2-D) model to reproduce the effects of three dimensional (3-D) in-ves sel components is proposed. Several issues in plasma control are exami ned to determine whether the 2-D model adjusted by this method reprodu ces the results of the 3-D model. Analyses are performed for the plasm a stabilization effects of in-vessel components, the evolutions of pla sma position and shape in plasma disturbances, the magnetic probe sign als and the stray fields at plasma breakdown. It is shown that this me thod of modifying 2-D models is acceptable for simulating plasma motio ns and probe signals. However, discrepancies between 3-D and 2-D model s are observed in the probe signals during rapid motions of plasmas an d stray fields at plasma breakdown. Plasma control issues, for which a ttention has to be paid to SD paths of eddy currents, are discussed.