Chemical erosion measurements from various carbon based limiters and coatings in TEXTOR-94

A well-diagnosed test limiter has been used in TEXTOR-94 to study - by means of spectroscopic techniques - the fluxes and the spatial distribution of hydrocarbons, which are formed by plasma interaction on carbon, silicon and titanium doped (SiC30, RGTi) graphites, B4C as well as from carbon coated metal limiters. On a special graphite limiter, which could externally be heated up to temperatures of 1400 K, the methane formation remained approximately constant up to 1050 K with a yield of about 3.5% and dropped well below 1% at 1350 K. Simultaneously the carbon ion fluxes into the plasma decreased by about 50%. By inserting the limiters deeper into the plasma the D-flux increased between 10(22)/m(2)s and 3 x 10(23)/m(2)s and the maximum methane production yield decreased to about 1%. On bulk doped graphites as well as Cu- and SS-limiters a similar methane formation behavior as pure graphite has been observed. However, a weak hydrocarbon formation rate is found for Mo- and W-limiters. No discrepancy between radial CH- and C-2-intensity profiles from injected and sputtered CH4 and C2H4 gas could be detected. The measured radial intensity profiles for CD were compared with a local erosion and deposition model (ERO-TEXTOR) using measured plasma parameters and atomic data taken from the Langer model. The calculations showed a reasonable agreement with the experimental results both in radial and toroidal direction.