Advancing Understanding of Plasma Facing Component Erosion in Fusion Devices: Insights from Optical Diagnostics and Reflections

Understanding erosion of Plasma Facing Components (PFCs) in fusion devices is critical for their efficient operation, particularly in long-pulse scenarios. This research focuses on validating models using synthetic optical diagnosis, specifically in the all-tungsten WEST tokamak. The study achieves quantitative agreement (within 20%) with experimental emission data for oxygen and tungsten across various sight-lines. A key finding is the substantial role of reflections: up to 95% of light from chamber limiters and ~50% from divertor targets. A power scan was completed (0.5-3 MW injected) both experimentally and modeled allowing for erosion from both the main chamber and divertor to be investigated over the scan. The ray tracing code mitsuba3 is used along with the CAD geometry, addressing 3D effects and reflections off in-vessel components. It reveals that low-Z species like oxygen significantly contribute to tungsten sputtering from PFCs in WEST. By employing collisional radiative modeling (ColRadPy) and ray-tracing simulations, the study generates realistic synthetic images of emission lines (O II at 397 W I at 400.9 nm), aiding in understanding impurity sources and transport within the SOL plasma. Reflections will play a pivotal role in future fusion devices like SPARC and ITER, especially in detached divertor operations with highly localized emissions.

This work was funded under DE-AC05-000R22725