Comparing reduced delta-f and direct total-f gyrokinetic models in view of their core-edge coupling with the XGC code

The High-Fidelity Whole Device Modeling (WDM) project aims to model the whole device of tokamaks with core-edge coupled gyrokinetic simulation models [wdmapp.pppl.gov]. The coupling of core reduced delta-f and edge total-f gyrokinetic models could enable a significant speed-up of the whole device modeling simulations. Thus, it is interesting to compare these models in the core plasma and in the edge pedestal, in view of their coupling. Both of these models differ mainly due to presence of the zeroth order term in the right hand side of the total-f gyrokinetic equation. This zeroth order term is responsible for driving a radial electric field associated with GAM-like oscillations. To investigate the coupling of these models, the subsequent expensive gyrokinetic 3D turbulence simulations have been performed starting from an already saturated gyrokinetic axisymmetric equilibria (collisions are not included). This work has also been extended to couple different axisymmetric and turbulent models available in XGC. It is shown that the radial electric field and its drive have to be taken care of consistently while coupling different models together. Furthermore, a comparison of reduced delta-f and total-f models with the heat source has also been discussed, by running gradient-driven and flux-driven simulations.