Effects of strike point location and collisional processes on energy and particle detachment in EAST with lower tungsten divertor

Divertor detachment is crucial for the particle and power exhaust in future fusion reactors. The EAST lower tungsten divertor, with its ‘corner slot’ structure, exhibits remarkable geometric closure, thus enhances neutral trapping. In this work, SOLPS-ITER modelling based on EAST experiments is conducted to explore the underlying mechanisms of the effects of strike point location on energy and particle detachment. Three H-mode cases with strike point locations on horizontal target, corner and vertical target are selected for investigation. The comparisons of detachment thresholds between the three cases via density scan modelling demonstrate satisfactory consistency with experiments. It is found that among three cases the horizontal target case has the lowest detachment threshold. This is attributed to recycled neutrals accumulating in the closed corner to form a neutral cushion with intense neutral-plasma interactions, where energy and momentum losses are more significant. Furthermore, the energy and momentum losses are closely linked, and the correlation between volumetric losses and target temperature is established. Additionally, the contributions of different collisions on energy and momentum balance in particle detachment regime are quantitatively evaluated. The simulations indicate that atom-plasma charge exchange collision make significant contributions to momentum loss, thus reducing the ion flux to target; while molecule-plasma elastic collision plays a key role in the closed corner with strong molecule accumulation. Molecule-associated recombination also provides a potential volumetric recombination channel to reduce the ion target flux. This study improves the understanding of strike-point location and neutral-plasma collisions on momentum and energy detachment, which is important for divertor optimization and heat flux control, supporting long-pulse detachment operation in EAST.