10th International workshop on "Stochasticity in Fusion Plasmas (SFP)"-"3D physics in stellarators and tokamaks"

Predicting the incident heat flux in future tokamaks, like ITER, is crucial to avoid divertor damage. Non-axisymmetric shaping of plasma facing components (PFCs) is a new technique to avoid e.g. melting of leading edges. Applied 3D perturbation fields are commonly used for plasma control. Both create toroidal asymmetries in the divertor heat flux patterns, which is the focus of this work. For perturbed plasmas, a heat flux model based on guiding center particle drift in vacuum fields [A. Wingen et al., NF 61, 016018 (2021)] is presented. It includes intrinsic and applied 3D magnetic fields as well as scalar electric potentials. For ions, divertor footprints are simulated for multiple kinetic energies and combined based on their respective contribution to the ion's Maxwellian distribution. For electrons, three different models are considered: a convection model like the one used for ions, a conduction model facilitated by collisions, and a heuristic 3D layer approach. The modeled divertor heat flux pattern is compared to infrared camera measurements with good agreement. Furthermore, it is found that ExB flow reduces the edge stochastization and strike point splitting. Introducing an additional sheath potential has only minor impact on the heat flux.



On NSTX-U it has been proposed to use a sawtooth-like profile in the toroidal direction for divertor tiles to shadow leading edges of neighboring tiles from incident heat flux. A new toolset, called HEAT, was developed to model the effect of 3D shaped PFCs. The tool uses a CAD model of the inner wall with all gaps, and traces heat flux from an axisymmetric EFIT equilibrium to the wall, assuming an Eich scaling [Eich et al., PRL 107, 215001 (2011)] of the heat flux layer width. It is planned to add the 3D heat flux model to the HEAT toolset in the future. The work is supported by US DoE under DE-AC05-00OR22725, DE-AC02-09CH11466 and DE-FC02-04ER54698.