Influence of Coulomb collision models and resonant magnetic perturbations on NBI fast ion loss and distribution on EAST

In tokamak plasmas, both Coulomb collisions and Resonant Magnetic Perturbations (RMPs) play a critical role in the loss of Neutral Beam Injection (NBI) fast ions. We have upgraded the Coulomb collision module in the Monte Carlo orbit-following code GYCAVA. The upgraded version of GYCAVA has been used to investigate the effects of the Coulomb collision model and the RMP toroidal mode number on NBI fast ion losses and heat loads in the EAST tokamak. Compared to the original Coulomb collision model in GYCAVA, which adopted the high-energy approximation and the Coulomb logarithm approximation, the upgraded model offers improved accuracy by eliminating these simplifying assumptions. Simulation results indicate that without the ripple field, the Coulomb logarithm approximation underestimates fast ion loss fractions, whereas the high-energy approximation has a negligible impact on losses. Increasing the effective charge number induces an asymmetric variation in the spatial distribution of fast ion loss regions; the enhancement of losses on the low-field side is substantially more pronounced than that on the high-field side. Regarding the RMP effect, the toroidal periodicity of the heat load distribution agrees with the RMP toroidal mode number. In the presence of the toroidal field ripple, simulations with the vacuum RMPs show substantially higher losses for n=2 RMPs compared to n=4 RMPs. However, when the plasma response effect is included in the simulations, the fast ion loss fractions for n=2 and n=4 RMPs become comparable.