Model based optimization and estimation of the field map during the breakdown phase in the ITER tokamak

The design of a breakdown scenario in a modern tokamak requires the optimization of Poloidal Field coils voltages and currents to guarantee a desired electric field and a low value of the poloidal field in a given region of the vacuum chamber in the presence of several operating constraints and limitations. The optimization problem can be approached in the discrete time domain and converted into a quadratic programming problem with linear constraints. In tokamaks like ITER, breakdown conditions are reached with very large currents in the metallic passive structures. If the field map has to be reconstructed for monitoring and control purposes, the estimation of such currents is very important and can be obtained by means of magnetic measurements. A Kalman Filtering approach is proposed to reconstruct eddy currents also in the presence of uncertainties on self and mutual inductances, currents to fields/fluxes relationships. Numerical simulations are presented on an early operation ITER breakdown scenario.