Experimental and numerical studies of separatrix splitting and magnetic footprints in DIII-D

A numerical field line integration code is used to study the structure of divertor footprints produced by small non-axisymmetric magnetic perturbations in the DIII-D tokamak. The modeling results are compared to experimental data which show a splitting of the divertor target plate heat flux into several distinct peaks when an n = 3 magnetic perturbation from the DIII-D I-coil is applied. The splitting consistently appears when the n = 3 perturbation is applied and disappears when the perturbation is removed. The magnitude of the splitting implied by the modeling is a factor of 2–3 smaller than the splitting seen in the experimental data. These results suggest that the plasma response to the applied n = 3 edge resonant magnetic perturbation amplifies the vacuum magnetic footprint structure on the divertor target plates. These results may have significant implications for the ITER divertor design.