GEM development for the spatial core-edge coupling of the PIC gyrokinetic codes GEM and XGC*

Within the Exascale Computing Program, the High-Fidelity Whole Device Modeling project aims at delivering a first-principles-based computational tool that simulates the plasma neoclassical and turbulent dynamics from the core to the edge of the tokamak. To permit such simulations, the different gyrokinetic codes need to be coupled. My work focuses on the coupling of two particle-in-cell (PIC) gyrokinetic codes, GEM and XGC. 

The coupling scheme initially implemented for XGC-XGC coupled simulations has been applied to GENE-GENE and GEM-GEM runs. These simplified core-couplings allowed us to learn about the behavior of the coupled system. The coupling of the continuum code GENE and the PIC code XGC has already started yielding results. Here, the first results obtained with the coupled PIC gyrokinetic codes, GEM and XGC, will be presented. For the coupling of GEM and XGC, besides the interpolation on different grids, exchange of particle information between the two will be attempted in order to maintain accurate particle dynamics.

In addition, for a more efficient coupling, the GPU optimization for GEM is ongoing and the first results will be also presented.