Quantification of deuterium and low-Z impurity deposition on long-term samples exposed in ASDEX Upgrade

Long Term Sample (LTS) holders installed at remote wall locations of ASDEX Upgrade (AUG) and equipped with silicon wafer witness samples are used to monitor the integral net deposition of boron by glow discharge boronisation (GDB). Deposited low-Z impurities (B, C) and deuterium are quantified by 3 He Nuclear Reaction Analysis. Isotopes are resolved by analysis of their characteristic peaks in the energy spectra of detected protons. For the analysis a fitting procedure, tailored to the expected species, has been implemented and calibrated against quantitatively characterised standard samples. The analysis has been applied to LTS from recent AUG campaigns. The results revealed that only a small fraction of the total boron introduced during the campaign can be accounted for with the rest assumed to be exhausted as molecular compounds during the campaign and also during post-campaign flushing of the vessel with air. • A dedicated NRA fitting procedure enables isotope-resolved quantification of D, B, C and O. • In ASDEX Upgrade, only about 4% of boron from GDB remains on remote wall surfaces. • Strong spatial asymmetries in B, D, C and O deposition are observed across wall locations. • Remote-wall deposits evolve towards a quasi-stationary thickness limited by re-erosion. • Deuterium saturation in B+C layers suggests boronisation will not drive rising T inventory in ITER.