A dedicated experimental programme has been initiated at the TEXTOR tokamak aiming at the assessment of a long-range fuel migration into the bulk of carbon-based materials. Three materials (former ITER reference CFC NB31, JET CFC DMS780 and fine-grain graphite EK98) were simultaneously exposed in the erosion-dominated zone of the scrape-off layer plasma in a series of reproducible discharges with a total duration of 177 s. The stripes made of corresponding materials were mounted at a roof-like test limiter. The tip of the limiter was exposed to a fluence of Φ~3•1025 D/m2 with a radial decay length of the fluence of 12 mm leading to fluencies of about Φ~2•1024 D/m2 at the far SOL edge of the limiter. The bulk temperature of the material was kept at ~500 K during the exposure.
The samples were analysed post-mortem by thermal desorption spectrometry (TDS) and nuclear reaction analysis (NRA) with a standard size 3He-beam (~1 mm diameter) as well as with a 3He-microbeam (~1 µm diameter).
The TDS analysis of the samples showed a similar deuterium retention for both CFC materials and a retention lower by ~20-30% for the fine-grain graphite. The amount of retention of (2-3)•1021 D/m2 for the highest fluences is in good agreement with the available database from ion beam facilities and plasma simulators for the given bulk temperature. In the range of fluences the materials were exposed to, the dependence of the retention on the fluence is close to ~Φ0.5, no sign of a saturation of the retention was observed. The estimations for TEXTOR show, that for the duration of the experiment the amount of deuterium retained in graphite (and similarly in CFCs) is by a factor of ~3 lower than that of deuterium co-deposited in carbon layers. However, the retention in co-deposited layers scales linearly with the fluence and thus would dominate on long-term scales.