Modelling of NBI shine-through in ITER non-nuclear phase to limit heat fluxes on first wall

Abstract

The occurrence of localized high heat fluxes on the ITER first wall can limit the lifetime of plasma-facing components. This can be the case of excessive shine-through losses due to high-energy Neutral Beam Injection (NBI) in low density plasmas, as in the first operation phases of ITER. The use of ITER NBI will be therefore limited to densities that guarantee acceptable power fluxes on the first wall. In this work, we review the NBI shine-through issue in the ITER pre-fusion phases by numerical simulations, extending previous modelling assumptions and exploiting the IMAS modelling framework. The dependencies of shine-through on beam injection energy and plasma density profiles are discussed and a heuristic formula for shine-through fraction is proposed, fitting a large database of ad-hoc simulations. In particular the effect of NBI vertical tilt is properly taken into account by considering the effect of different plasma density profile shapes. Both on- and off-axis ITER H neutral beam injection are considered in the study. We show that increasing the density peaking, ITER NBI shine-through losses decrease, with magnitude depending on the beam vertical tilt. Two ionization codes, NEMO and BBNBI, are compared exploiting the standardized data input of the IMAS suite.