Controlling magnetic footprints wetted area using resonant magnetic perturbations

The radial extension of the heat load distribution at the divertor plates due to 3D magnetic fields of a tokamak is determined by the resonant component of the non-axisymmetric field perturbations. Whether they are intrinsic, like error fields, or they are applied through 3D coils, the non-axisymmetric fields produce complex 3D edge magnetic topologies that alter the properties of the heat and particle flux distributions on the target plates. A study of the impact of applied 3D fields on the footprints wetted area is done for the DIII-D tokamak for several equilibria using the MHD code M3D-C1 coupled with the field line tracing code TRIP3D. To highlight the impact of the resonant component of the magnetic perturbation (MP) versus the non-resonant one, the poloidal spectrum of the MP is modified by varying the relative phase of the 2 rows of 3D coils used to produce n<3 perturbation. This shows that the largest footprint is achieved when the relative phase of the 2 rows is close to zero, that corresponds to the maximum resonant coupling with the plasma. A comparison of the predictions with experimental data from particle flux and infrared images is also shown. Work supported by US DOE under DE-FC02-04ER54698, DE-FG02-07ER54917 and DE-FG02-05ER54809.