Evaluation of upper divertor impurity sourcing and transport across different plasma shapes in the WEST tokamak

The WEST tokamak operates with long pulses and tungsten (W) walls, 2 key aspects of future tokamaks. This makes it the ideal machine to identify impurity sources that will be degrade the performance of future devices. In WEST, it was found that the core W concentration is uncorrelated with measured W and light impurity sources from the lower divertor, indicating higher W leakage to the core than expected. A series of shots were performed in the C11 (2025) campaign to investigate if the poorly-screened upper target is a source of this leakage. To do this, each shot featured four shape changes that varied the distance between the separatrix and the upper target. Initial analysis of each shape suggests other impurity sources other than the lower targets, prompting usage of modelling to identify them. To do this, each shape is modelled in the edge plasma transport code SOLEDGE3X in 2D. The shapes are recreated using flush mounted and reciprocating Langmuir probe data as constraints to the target and upstream plasma conditions respectively. Kinetic neutrals using EIRENE and drifts were included in the simulation to approach realistic experimental conditions. The W sputtering yield at the upper target was calculated using the revised Bohdansky formula using the conditions at each wall element. A sensitivity analysis using different combinations of the characteristic light impurities was performed to identify the impact of each on the plasma.