SOLPS-ITER Wide Grid implementation in different divertor geometries

Simulations of DIII-D SAS divertor and MAST-U Super X configuration using the Wide Grid version of SOLPS-ITER with kinetic neutral transport are compared with standard SOLPS-ITER 3.0.8 simulations , and with simulations with 9-point-stencil fluid neutrals.

The standard B2.5 grids limit the contact of the plasma to the targets, while wide grids allow particle and heat loads onto other elements, such as the main chamber walls or limiter surfaces, to be captured. This enables estimation of neutral production (recycling and sputtering) from the first wall components, and avoids an artificial vacuum region in the far-SOL which overestimates neutral mean free paths. Additionally, intersecting elements within the divertor region may either force the creation of very narrow classical computational grids or the modification of the divertor geometry to avoid such issue. This can result in solutions that depend on the boundary conditions selected for the outer radial surfaces, which are poorly constrained by physical processes. With wide grids, the correct divertor geometry can be used without a strong influence of boundary conditions on the near Scrape-Off Layer.