Simulations of divertor heat flux width using transport code with cross-field drifts under the BOUT plus plus framework

The fluid transport code [trans-electric field (Er) module] under the BOUT++ framework has been used to simulate divertor heat flux width and boundary Er with all drifts and the sheath potential in the scrape-off layer. The calculated steady state radial Er in the pedestal region has been compared with that of experimental measurements from the Alcator C-Mod tokamak. The magnitude and shape of Er are similar to those of the experimental data. In order to understand the relative role of cross-field drifts vs turbulent transport in setting the heat flux width, four C-Mod enhanced D-alpha H-mode discharges with a lower single null divertor configuration should be simulated. BOUT++ transport simulations with cross-field drifts included yield similar heat flux width lambda(q) to that of experimental measurements (within a factor of 2) from both the probe and the surface thermocouple diagnostics and show a similar trend with plasma current to that of the Eich experimental scaling. The simulations show that both drifts and turbulent transport compete to determine the heat flux width. The magnetic drifts play a dominant role in setting the divertor heat-flux width, while the E x B drift decreases the heat flux width by 10%-25%, leading to improved agreement with the experiment relative to Goldston's model. A turbulence diffusivity scan (chi(perpendicular to)) identifies two distinct regimes: a drift dominant regime when chi(perpendicular to) is small and a turbulence dominant regime when chi(perpendicular to) is large. The Goldston heuristic drift model yields a lower limit of the width lambda(q). (c) 2020 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).