Hydrogen isotope depth profiling in carbon samples from the erosion dominated inner vessel walls of JET

In order to investigate the hydrogen isotope accumulation at the erosion dominated inner walls of fusion experiments, several small carbon samples have been mounted in the inner wall tiles of the torus of the JET Joint Undertaking. After about 2.5 years of JET operation, including the extended D/T phase and the D/D cleaning phase, the samples have been removed and analysed by RBS, ERDA and AMS. In the near surface region only small T concentrations are measured. A much larger T concentration is found at depths between about 1 and 2 μm. This may originate from energetic (∼1 MeV) T which is produced during the D/D discharges and implanted to large depth. The lower energy (keV) T which is implanted during the D/T discharges became effectively removed from the inner wall, by isotope exchange with implanted D or H and/or by erosion of the wall. The total amount of T within a depth of about 2 μm was found to be about 1–3×1013 T/cm2, while in a surface layer of about 0.5 μm about 1–3×1012 T/cm2, about 2–4×1016 D/cm2 and about 4–9×1016 H/cm2 were measured.