Analyzing the effects of reflections on optical diagnostics in the main chamber and divertor of WEST (invited).

Understanding the erosion of plasma facing components in fusion devices is vital, particularly for long-pulse operations. This study presents the application of synthetic optical diagnosis on the all-W WEST tokamak. The analysis reveals reflections as significant contributors to measured emission, varying across main chamber limiters and divertor targets. Reflections at divertor locations can be up to 50% of measured emission while 95% at limiter locations. Oxygen is investigated as a proxy for low-Z species and underscores the importance of reflections in interpreting optical diagnostics, especially for validating plasma-material interactions and scrape-off layer impurity transport codes. As more fusion devices adopt full metal walls, the accurate assessment of reflections will become increasingly crucial for erosion analysis and plasma control.