Quantitative hydrogen analysis in fusion-relevant materials by SIMS

In fusion reactors graphite brazed on metallic substrates is commonly used for plasma-exposed components of the First Wall. Exposed to high heat-, hydrogen- and deuterium-fluxes, the stability of the braze under such conditions is essential. A sample of graphite brazed with zirconium on a molybdenum high temperature alloy was cut and exposed to a deuterium plasma (dose 1022cm-2). Secondary Ion Mass Spectroscopy (SIMS) has proven to combine high sensitivity to hydrogen and deuterium with the ability to perform depth profiling. Thus SIMS investigations should determine the extent of deuterium diffusion into the braze and the substrate. SIMS measurement conditions were optimized with special regard to energy filtering and to computer controlled magnetic field adjustment. Step scan measurements to obtain information on the surface concentration of deuterium and depth profiling to determine the distribution of the bulk concentration were performed. In the braze, directly exposed to the plasma, the deuterium content was up to a few atomic percent. The shielding of a thin graphite layer (0.5 mm) reduced the deuterium content to approximately 300 ppm at., but diffusion was still present. For deuterium quantification a homogenous graphite standard and molybdenum- and zirconium-implantation standards were used. With respect to the diffusivity of deuterium, MoD/Mo and ZrD/Zr ratios were measured. Different energy filtering was used to distinguish trapped and free deuterium. The comparison of experimental depth profiles with theoretical Monte Carlo simulations showed the effects of implantation damage in the bulk and of trapping. The relative sensitivity factors for deuterium in graphite, molybdenum and zirconium were calculated. (author)