COLORIMETRIC MEASUREMENTS OF CARBON EROSION AND DEPOSITION RATES ON EXTENDED AREAS OF PLASMA-FACING COMPONENTS IN TEXTOR

Colorimetry is introduced at TEXTOR as a technique to observe the carb on erosion on extended areas. It quantifies the interference colours o f thin (similar to 200 nm) transparent co-deposits of carbon and hydro gen which are mainly depending on thickness. The paper describes the f acility as a video and an image processing system and the thickness de termination by means of the colour coordinate hue (h(xy)). Erosion rat es up to -22 nm/s are measured on a precarbonized spherical graphite t est piece exposed in the SOL for neutral beam heated plasmas. Part of the carbon is redeposited promptly with +4 nm/s, but the transition ra nge between net erosion and deposition is not stationary. Erosion is o bserved around the tangency point. Beyond 2 cm into the SOL, depositio n is found to be influenced by the limiter geometry.