Progress towards modeling tokamak boundary plasma turbulence and understanding its role in setting divertor heat flux widths

The heat flux distributions on divertor targets in H-mode plasmas are serious concerns for future devices. We seek to simulate the tokamak boundary plasma turbulence and heat transport in the edge localized mode-suppressed regimes. The improved BOUT++ model shows that not only I_p but also the radial electric field E_r plays an important role on the turbulence behavior and sets the heat flux width. Instead of calculating E_r from the pressure gradient term (diamagnetic E_r), it is calculated from the plasma transport equations with the sheath potential in the scrape-off layer and the plasma density and temperature profiles inside the separatrix from the experiment. The simulation results with the new E_r model have better agreement with the experiment than using the diamagnetic E_r model: (1) The electromagnetic turbulence in enhanced D_α H-mode shows the characteristics of quasi-coherent modes (QCMs) and broadband turbulence. The mode spectra are in agreement with the phase contrast imaging data and almost has no change in comparison to the cases which use the diamagnetic E_r model; (2) the self-consistent boundary E_r is needed for the turbulence simulations to get the consistent heat flux width with the experiment; (3) the frequencies of the QCMs are proportional to E_r, while the divertor heat flux widths are inversely proportional to E_r; and (4) the BOUT++ turbulence simulations yield a similar heat flux width to the experimental Eich scaling law and the prediction from the Goldston heuristic drift model.