Effect of ideal internal MHD instabilities on NBI fast ion redistribution in ITER 15 MA scenario

Abstract

Abstract Transport of fast ions is a crucial issue during the operation of ITER. Redistribution of neutral beam injection (NBI) fast ions by the ideal internal magnetohydrodynamic (MHD) instabilities in ITER is studied utilizing the guiding-center code ORBIT (White R B and Chance M S 1984 Phys. Fluids 27 2455). Effects of the perturbation amplitude A of the internal kink, the perturbation frequency f of the fishbone instability, and the toroidal mode number n of the internal kink are investigated, respectively, in this work. The n = 1 internal kink mode can cause NBI fast ions transporting in real space from regions of 0 < s ≤ 0.32 to 0.32 < s ≤ 0.53 , where s labels the normalized plasma radial coordinate. The transport of fast ions is greater as the perturbation amplitude increases. The maximum relative change of the number of fast ions approaches 5% when the perturbation amplitude rises to 500 G. A strong transport is generated between the regions of 0 < s ≤ 0.05 and 0.05 < s ≤ 0.12 in the presence of the fishbone instability. Higher frequency results in greater transport, and the number of fast ions in 0 < s ≤ 0.05 is reduced by 30% at the fishbone frequency of 100 kHz. Perturbations with higher n will lead to the excursion of fast ion transport regions outward along the radial direction. The loss of fast ions, however, is not affected by the internal MHD perturbation. Strong transport from 0 < s ≤ 0.05 to 0.05 < s ≤ 0.12 does not influence the plasma heating power of ITER, since the NBI fast ions are still located in the plasma core. On the other hand, the influence of fast ion transport from 0 < s ≤ 0.32 to 0.32 < s ≤ 0.53 needs further study.