Linear and quasi-linear modeling in view of ELM control in MAST-U including effects of error fields

Edge localized modes (ELMs) pose a critical challenge to the safety and performance of plasma-facing components in tokamaks due to their periodic expulsion of heat and particles. This study investigates the behavior of various figures of merit for evaluating resonant magnetic perturbations (RMPs) as a tool for achieving ELM control in the spherical tokamak MAST-U. A combination of linear and quasi-linear modeling workflows, including MARS-F (single-fluid resistive MHD) and KilCA/QL-Balance (two-fluid kinetic) codes, was used to analyze plasma responses to RMPs under realistic operational conditions. To address recent experimental results, a detailed model for the n = 2 intrinsic error field (EF) generated by the Poloidal Field coil system was developed, and the plasma response to this EF was computed. Results indicate that the n = 2 EF is, at least, of the same order of magnitude as the perturbations introduced by the external RMP coils. In particular, the EF was found to significantly shift the optimal points of the analyzed metrics, affecting the effectiveness of ELM mitigation strategies and being detrimental to the core confinement when unfavorable aligned with the external RMPs, potentially explaining the observation of locked-modes. These results underscore the critical need for addressing intrinsic EF correction when designing ELM control strategies.