COLORIMETRY OF INTERFERENCE COLORS TO INVESTIGATE THICKNESS CHANGES OF PROTECTIVE COATINGS IN TEXTOR

Colorimetry is introduced at TEXTOR as a technique to observe the carb on erosion from protective coatings on wall elements. It quantifies th e interference colours of the transparent carbon and hydrogen containi ng films (a-C:H) which are mainly depending on thickness. The paper de scribes the setup and calibration of the facility as a video and an im age processing system and how colour coordinates are defined and measu red and discusses the influence of other parameters. In neutral beam h eated discharges, erosion rates up to -22 nm/s are measured on a preca rbonized test piece exposed in the scrape-off layer plasma. This corre sponds to a loss of 1.4 x 10(17) C/cm(2)s taking into account the carb on density of 6.5 x 10(22) C/cm(3) of a-C:H. Part of the eroded carbon is redeposited on the test piece with +4 nm/s. The thickness pattern is not stationary as time proceeds. Erosion is observed around the tan gent point. At locations further apart than 2 cm from the plasma edge, deposition is found influenced by the limiter geometry.