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

Abstract

Experiments in the plasma-wall interaction facility at TEXTOR have been carried out to compare (i) the local transport of 13CH4 and 13C2H4 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 13C. The analysis is twofold: spectroscopy was applied to follow up in situ the observable hydrocarbon break-up products (C2, CD, C+, and C2+), and post mortem analysis was used to determine the 13C 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 13C deposition efficiency shows a dependence on both the limiter material and on the injected hydrocarbon species.