The effects of resonant magnetic perturbations and charge-exchange reactions on fast ion confinement and neutron emission in the Mega Amp Spherical Tokamak

TL;DR

This study investigates how resonant magnetic perturbations and charge-exchange reactions affect fast ion confinement and neutron emission in MAST, using advanced modeling that aligns well with experimental data.

Contribution

The paper introduces an improved Monte-Carlo model including plasma response and charge-exchange effects to accurately simulate fast ion behavior under RMPs in MAST.

Findings

Neutron rates decrease significantly with RMP application.

Charge-exchange reactions critically influence neutron emission before RMPs.

Model results agree well with experimental measurements.

Abstract

The application of non-axisymmetric resonant magnetic perturbations (RMPs) to low current plasmas in the Mega Amp Spherical Tokamak (MAST) was found to be correlated with substantial drops in neutron production, suggesting a significant degradation of fast ion confinement. The effects of such perturbations on fast ions in MAST have been modelled using a revised version of a non-steady-state orbit-following Monte-Carlo code (NSS OFMC), in which the parametrization of fusion reaction rates has been updated and neutron rates have been recalculated. Losses of fast ions via charge-exchange (CX) with background neutrals and the subsequent reionization of fast neutrals due to collisions with bulk plasma particles have also been taken into account. The effects of the plasma response to externally-applied RMPs have been included in the modelling. The updated results show that computed neutron rates in the presence of RMPs with the plasma response and CX reactions taken into account agree very well with the experimental data throughout the analysis target time. CX reactions play an important role in determining the neutron rates, in particular before the onset of RMPs.