Chemical erosion in TEXTOR-94

In order to study the fluxes and the spatial distribution of hydrocarbons, which are formed by plasma interaction on limiters and walls of TEXTOR, bot h spectroscopic and mass analysis measurements have been performed. Spectro scopic diagnostic stations on specially designed limiter locks, where an ea sy replacement of limiters with different materials is possible, allowed th e determination of the hydrocarbon production from carbon, silicon and tita nium doped (SiC30, RGTi) graphites, B4C as well as carbon coated metal limi ters of copper, stainless steel, molybdenum, and tungsten. In addition a sp ecial carbon limiter was available, which could externally be heated up to temperatures of 1400 K and, therefore, allowed measurements on a homogeneou sly hot surface. It was found that the methane formation remained approxima tely constant up to 1050 K with a yield of about 3.5% and dropped well belo w 1% at 1350K. Simultaneously the carbon ion fluxes into the plasma decreas ed by about 50% for ohmically heated plasmas. The fluxes onto the limiters could be increased by an order of magnitude by inserting the limiter deeper into the plasma, which resulted in a drop of the maximum methane productio n yield to 1% at 3.10(23)/(m(2)s). Bulk doped graphites as well as Cu- and SS-limiters show a similar methane production behaviour as pure graphites, whereas for Mo- and W-limiters the hydrocarbon formation rate is low. A pro nounced isotope effect could not be detected. Photon efficiencies for the C H/D-band emission were calculated with a local erosion and deposition model (ERO-TEXTOR) taking into account the measured plasma boundary parameters a nd the atomic data from the Langer model. These calculations justify the ap plication of the factors used for the conversion of measured intensities in to CH/D-4 particle fluxes for TEXTOR limiter conditions.