Residual magnetic stray field in ITER building and field perturbation on the plasma due to ferromagnetic iron components outside the vessel

Abstract

The present work evaluates, using 3D finite element (FE) electromagnetic (EM) analyses, the poloidal field coil (PFC) stray field reduction inside and outside the main ITER building due to the presence of ferromagnetic content in the concrete and other iron components outside the vessel (mainly the huge iron boxes of the NBI – neutral beam injector – and the iron doors at the end of the port corridors). To perform these analyses a 360° 3D EM model of the ITER building has been developed, named electromagnetic model of the building complex (EMMOBC), which includes the poloidal field coils, the plasma, a coarse model of the two heating & current drive (H&CD) NBIs, the coils of the NBI active magnetic field reduction system, and all the main building components that could include ferromagnetic materials. The plasma scenarios at the start of flat-top (SOF) and at the end of burning (EOB) have been considered. The effect on the stray field on the NBI due to the presence of the active (AMFRS) and passive (PMFRS) magnetic field reduction system of the near NBI and of the others iron component in the building has been evaluated, using EMMOBC that include the coarse model of the two NBIs. The coil currents of the AMFRS in the H&CD NBI have been optimized for the stray field coming from the SOF and EOB plasma scenarios at plasma current of 15 MA. The stray field at SOF and EOB, including the effects of the ferromagnetic iron content (outside the vessel), has been evaluated inside and outside the main ITER building using the EMMOBC. Finally the field perturbation produced on the plasma q = 2 surface has been evaluated.