Optimizing beam-ion confinement in ITER by adjusting the toroidal phase of the 3-D magnetic fields applied for ELM control

TL;DR

This study uses detailed simulations to analyze how the phase of applied 3D magnetic fields affects fast-ion confinement in ITER, aiming to optimize RMP configurations for better NBI confinement without compromising ELM control.

Contribution

It demonstrates that the toroidal phase of RMPs significantly influences fast-ion losses and provides insights into the underlying physics mechanisms, aiding in RMP optimization for ITER.

Findings

Fast-ion losses depend on the poloidal spectra and toroidal phase of RMPs.

The toroidal phase does not affect ELM control capabilities.

Resonant transport layers and overlapping resonances contribute to ion losses.

Abstract

The confinement of Neutral Beam Injection (NBI) particles in the presence of n=3 Resonant Magnetic Perturbations (RMPs) in 15 MA ITER DT plasmas has been studied using full orbit ASCOT simulations. Realistic NBI distribution functions, and 3D wall and equilibria, including the plasma response to the externally applied 3D fields calculated with MARS-F, have been employed. The observed total fast-ion losses depend on the poloidal spectra of the applied n=3 RMP as well as on the absolute toroidal phase of the applied perturbation with respect to the NBI birth distribution. The absolute toroidal phase of the RMP perturbation does not affect the ELM control capabilities, which makes it a key parameter in the confinement optimization. The physics mechanisms underlying the observed fast-ion losses induced by the applied 3D fields have been studied in terms of the variation of the particle canonical angular momentum ($\delta P_{\phi}$) induced by the applied 3D fields. The presented simulations indicate that the transport is located in an Edge Resonant Transport Layer (ERTL) as observed previously in ASDEX Upgrade studies. Similarly, our results indicate that an overlapping of several linear and nonlinear resonances at the edge of the plasma might be responsible for the observed fast-ion losses. The results presented here may help to optimize the RMP configuration with respect to the NBI confinement in future ITER discharges.