The BOUT++ edge plasma transport code is applied to study the effects of neutral recycling, drifts and heating scheme on edge plasma profiles and the divertor heat flux width of two discharges of the experimental advanced superconducting tokamak (EAST) steady-state H-mode plasmas heated by low hybrid wave (LHW) and neutral beam (NB), respectively. Neutral recycling seems to have played an important role in the plasma density profile. The edge plasma density drops dramatically for the case w/o neutral recycling, while it can be sustained for the case w/ neutral recycling. Drifts are found to have significant influences on edge plasma profiles. Both the amplitude and width of the divertor heat flux are found to have increased a lot due to drifts. The simulated heat flux width w/ drifts for the two discharges shows reasonable agreement with the experiments. However, the width from the simulation and experiment for the LHW heated discharge is much larger than that of the NB heated discharge. Comparison with Goldston’s drift-based model and more detailed analysis on the heat flux contributions from drifts versus turbulence show that drifts are the dominant factor in edge plasma transport for both LHW and NB heated discharges, while turbulence may have played a more important role in determining the heat flux width in LHW heated discharges than that in NB heated discharges. This may account for the larger heat flux width in the LHW heated discharge. The magnetic topology and the equilibrium change by the LHW power may also be a potential reason for the larger heat flux width in the LHW heated discharges, which still needs more evidence and studies to support it. Additional SOLPS simulation w/o drifts for the two discharges show reasonable agreement with the counterpart from the BOUT++ simulation, suggesting the two are both suitable codes for EAST edge plasma simulation.

A conventional single null divertor geometry has been proposed for Chinese fusion engineering testing reactor (CFETR) with fusion power up to gigawatt level. Modeling using the SOLPS5.0 code package shows promising results for divertor power exhaust by seeding with neon (Ne) and deuterium (D2). Partial detachment for both inner and outer divertor targets can be achieved with a peak heat load lower than 3 MW/m2. The effective ion charge number, Zeff, at the core boundary is below three, which can be further reduced by increasing the upstream D2 puffing rate. A higher D2 puffing rate helps to increase electron density (ne) in scrape-off layer (SOL) and the impurity screening ability. Based on the SOLPS modeling results, the lifetime of tungsten (W) divertor targets has been estimated by using the DIVIMP code, which indicates that W sputtering is mainly contributed by Ne ions at a far SOL region due to high electron and ion temperature (Te and Ti) there. Upstream D2 puffing can reduce the W erosion rate and W impurity concentration inside the separatrix due to decreasing Te and Ti at the far SOL region. The modeling results show a viable operation regime for the CFETR divertor.