Linear and quasi-linear modeling in view of ELM control in MAST-U: effects of Error Fields and pedestal characteristics
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 (twofluid 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 (PF) 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 of 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. The study further explores the dependence of ELM control on kinetic parameters through a systematic scan of the pedestal density profile. Findings reveal that different metrics exhibit varying degrees of robustness to changes in the density gradient. While radial field-based and torque-based metrics optima are found to be more solid, displacement-based metrics are more sensitive to variations, emphasizing the importance of accurate equilibrium reconstruction and robust kinetic modeling. These results underscore the critical need for addressing intrinsic EF correction and integrating kinetic considerations when designing ELM control strategies.