Prediction of Divertor Heat Flux width on ITER and CFETR Using BOUT++*

Investigation on the turbulent transport dynamics in Scrape-off-layer (SOL) and divertor heat flux width prediction is performed for ITER and China Fusion Engineering Test Reactor (CFETR). Both BOUT++ transport and turbulence codes are applied to capture the physics on different spatial-temporal scale. Simulations start with ITER 15MA baseline scenario and CFETR R7.2 Hybrid scenario (R=7.2m, B_T =6.5T) respectively. In BOUT++ transport code, parametric scan for the SOL anomalous thermal diffusivity is performed which shows that when diffusivity is smaller than a critical value, heat flux width is almost unchanged, which is roughly consistent with Goldston’s HD model. Otherwise it would increase following the square-root of diffusivity scaling, indicating a transition from drift dominant regime to turbulence dominant regime. Using BOUT++ 6-field turbulence code, pedestal structure is found to be important in determining the effective SOL thermal diffusivity and in setting divertor heat flux width. Radial transport by electro-magnetic turbulence spreading is found to be the main contributor of the transport across separatrix in these turbulence simulations.