Time resolved observation of the erosion of boron containing protective coatings on wall elements of TEXTOR-94 by means of colorimetry

The paper describes the investigation of the progressive erosion of an a-B:D coated test piece during 22 pulses in the SOL of TEXTOR-94. Time resolved observations by colorimetry reveal that the erosion proceeds in steps: during an intermediate phase the rates do not exceed ∼ − 1.5 nm/s. Thereafter they jump to about −6 nm/s. This is due to carbon incorporation and triggered when the concentration approaches ∼ 40%. The changing composition may influence the ratio of the BII/CII emission near the surface. The process ends with a carbon rich layer on the remnants of the boron film. Combination of different investigations (AES, NRA, EPMA) results in a preliminary model description.