Effects of local toroidal field ripples due to test blanket modules for ITER on radial transport of thermal ions

Abstract

The effects of local toroidal field (TF) ripples due to ferromagnetic steels used in test blanket modules (TBMs) in ITER on the radial transport of thermal ions located near the top of the pedestal are investigated using a fully three-dimensional magnetic field orbit following Monte Carlo (F3D-OFMC) code. In the simulation, the three-dimensional motion of 20 000 test particles, distributed near the top of the pedestal (ΨN = 0.91) with the same Maxwellian velocity distribution as the thermal ions at this location, is traced for 1.9 s. In comparison with the number of lost particles in the case without a TBM, the additional loss with three TBM ports expected in ITER is evaluated to be less than 1% of the test particles. The additional losses increase linearly with the number of TBM ports and with the square of the amplitude of the local TF ripple. The poloidal structure of the TF ripple without ferritic inserts and a case with 18 TBM ports are also compared. It is found that cases having the same ripple amplitude at a certain point can have substantially different additional loss rates if the poloidal ripple structure is not the same. The ripple amplitude near the banana tip seems to be the most important factor in determining the radial diffusion of thermal ions.