Computational Exploration of RMP-Scrape-Off Layer Broadening

A theoretical explanation for experimental observations in DIII-D is provided, showing that the effectiveness of resonant magnetic perturbations (RMPs) in assisting the broadening of the scrape-off layer (SOL) depends critically on the strength and spectrum of the applied field. Two experiments applying MPs to influence edge shear and promote turbulence spreading are examined computationally: While one configuration led to a reduction in ExB shear and a broadened heat flux profile, a second experiment did not, prompting a need for modeling. Using the M3D-C1 resistive MHD code to compute magnetic response and coupling it to the Hermes-3 turbulence code, the observed difference between the two modeled cases is reproduced. Modeling indicates that the less effective case lacked sufficient perturbation strength and proper timing relative to the L-H transition. This computational study was motivated by recent experimental efforts in inducing turbulence-broadened power scrape-off widths through RMPs and aims to guide future experiments toward more effective SOL broadening. The work demonstrates that simulation-informed MP design can increase turbulence levels in the edge, opening a path to mitigating heat flux to the divertor in reactor-relevant plasmas.