Predictions of divertor heat load under resonant magnetic perturbations

Resonant magnetic perturbations (RMPs), the primary technique for edge localized modes (ELMs) mitigation and suppression on current and future tokamaks, break tokamaks' toroidal symmetry. Many of the widely used tokamak transport models based on axisymmetric assumption nowadays are hence not applicable for edge and divertor modeling with RMPs. Recently, BOUT++'s transport model has been extended to incorporate 3D plasma response field from RMPs. Provided by nonaxisymmetric equilibrium code GPEC, this field is often four orders of magnitude smaller than the axisymmetric field, i.e., $| ilde{B}_{rmp}/B_0|<10^{-4}$. Thus, it is treated as a higher order modification to the equilibrium magnetic field in the plasma transport equations. This small perturbation term has a profound influence on divertor heat loads. Preliminary test shows a distinct striation pattern appears on the divertor targets once the RMPs field is turned on. The new 3D extension of BOUT++ not only enables the 3D divertor plasma transport capability but also opens a path to study edge plasma instability and turbulence dynamics with RMPs.