Deuterium retention in Be:N:D codeposits

Nitrogen seeding can be a viable tool for controlling local heat fluxes in the divertor, but its compatibility with Beryllium as first wall material has to be proven and especially the effect on fuel retention has to be understood if it is to be used with deuterium/tritium plasma. Therefore, codeposited material was collected when Be targets were exposed to nitrogen-seeded D-plasmas in PISCES-B. The collected Be:N:D codeposits were analyzed with nuclear reaction analysis (NRA) and thermal desorption mass-spectroscopy. The D/Be ratios in the deposits formed at 300 K were between 0.1 and 2, scale with the Be deposition rate as rD−0.7 and scale linearly with the energy of the incident D. Normalized D/Be ratios are not influenced by the N seeding rate. The N/Be ratios were between 0.1 and 0.3, are virtually independent from the D neutral energy or N seeding level, and show only a weak rD−0.17 dependence. Re-examining samples out-gassed to 920 K with NRA, show that more than half of the N but less than 5% of the D remain in the layers