Comparison of 13C2H4 and 13CH4 injection through graphite and tungsten limiters in TEXTOR

Experiments in the plasma-wall interaction facility at TEXTOR have been carried out to compare (i) the local transport of (CH4)-C-13 and (C2H4)-C-13 injected through a gas aperture implemented in spherical limiters made of polycrystalline tungsten and fine-grain graphite and (ii) the properties of local deposited carbon layers on the polished limiter surface. Each limiter was positioned in the scrape-off layer and exposed to ten identical ohmic deuterium discharges of 4s length-accumulating 40 plasma seconds. The injection rates were normalized to the amount of injected C-13. The analysis is twofold: spectroscopy was applied to follow up in situ the observable hydrocarbon break-up products (C-2, CD, C+, and C2+), and post mortem analysis was used to determine the C-13 deposition efficiency. The penetration depths of hydrocarbon break-up products in the plasma were determined. Significant CH emission was observed in front of W limiter prior to injection. The C-13 deposition efficiency shows a dependence on both the limiter material and on the injected hydrocarbon species.