Using variations in divertor magnetic topology and geometry to optimize divertor detachment

Total flux expansion, a divertor magnetic topology design choice embodied in the Super-X divertor, is predicted through simple analytic models and SOLPS calculations to reduce the plasma and impurity density detachment thresholds as the outer divertor target strike point position, Rt, is increased. Since the total magnetic field, |B| ~ 1/R, |B| at the target is lowered as Rt is increased. Those predictions are contradicted by recent TCV experimental results. The SOLPS-ITER code was utilized to both match TCV results and determine, more generally, the relative effect of detachment threshold by 'magnetic topology' (in this case, total flux expansion) and 'divertor geometry', for which we vary a) the separatrix incidence angle to the divertor surface and b) the effect of physical baffles that retain more neutrals in the divertor.