Measuring the multimodal plasma response in MAST-U

MARS-F simulations of plasma response in MAST-U highlight the possibility to directly measure the changes in plasma response as a function of the applied 3D field poloidal spectrum, in order to identify the best coil configuration to achieve ELM suppression. Achieving ELM suppression in spherical tokamaks by applying resonant magnetic perturbation (RMP) has proven challenging. The poloidal spectrum of the applied RMP is a key parameter that has an impact on the capability to mitigate and eventually suppress ELMs. In this work the resistive MHD code MARS-F is used to evaluate the possibility to measure directly the plasma response in MAST-U, and particularly its variation as function of the applied poloidal spectrum, in order to experimentally validate the predicted best RMP configuration for ELM suppression. Toroidal mode number n=2 RMP is considered to minimize the presence of sidebands, and to avoid the deleterious core coupling of n=1. Singular Value Decomposition is used to highlight linearly independent structures in the simulated magnetic 3D fields and how those structures can be measured at the wall where the magnetic sensors are located. Alternative ways to measure the multimodal plasma response and how they can be used to infer the best RMP configuration to achieve ELM suppression are also presented, including the plasma displacement and the 3D footprints at the divertor plates.