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. (c) 2007 Elsevier B.V. All rights reserved.