Overview of the emissivity measurements performed in WEST: in situ and post-mortem observations

Abstract This paper summarizes the emissivity measurements performed on plasma-facing units (PFU) of WEST lower divertor during first phase running with a mix actively cooled ITER-like PFUs made bulk tungsten (W) and inertially graphite coating tungsten. In situ assessments laboratory after removing W-coated ITER-grade from device are shown. The exhibit complex pattern strong variation as function space time mainly explained magnetic equilibrium (strike point location) well plasma performances experimental campaigns. exposed PFU exhibits sharp spatial 0.05 to 0.85 at monoblock scale (12 mm) transition erosion deposition (next strike areas high-field side. On low-field side, varies 0.12 location, 0.2 few cm away in low-field-side direction. range exposure is much higher than unexposed 0.09 0.15. observation shows rapid evolution, typically pulses, inner outer location. whole distribution discussed its due operation start-up removal components.