Simulations of divertor heat flux widths using BOUT++ transport code with drifts*

The BOUT++ fluid transport code has been developed with all drifts and the sheath potential in the SOL. The calculated steady state radial electric field (E_r) has been compared with experimental measurements from a C-Mod discharge using charge exchange recombination spectroscopy. The simulated E_r profile is similar to the main ion diamagnetic term inferred from Thomson scattering profiles of electron temperature and density. In order to understand the impacts of drifts vs. turbulent transport on the divertor heat flux width, a set of four C-Mod EDA H-mode discharges with lower single null divertor configuration are simulated. BOUT++ transport simulations with all drifts included yield similar divertor heat flux width to experimental measurements varying within a factor of 2 and show a similar trend to the Goldston’s HD model. Magnetic drift has a significant influence on the divertor heat-flux widths, while the ExB drift further decreases the heat flux width by 10%~25%. In simulations of C-Mod discharges, the drifts dominate the cross-field transport and the heat flux width is sensitive to the separatrix electron temperature.