Deuterium Retention Studies in Ion Beam Damaged W

(1) Los Alamos National Laboratory, P.O. Box 1663, Los Alamos, NM, 87545, USA
(2) University of California San Diego, 9500 Gilman Drive, La Jolla, CA, 92093-0417, USA

The trapping and retention of tritium fuel within neutron damaged plasma facing components (PFCs) is of primary concern to next step fusion devices [1]. Tungsten is the principal plasma facing material candidate for first wall and divertor armor due to its high melting point, low H isotope retention, and excellent resistance to sputtering. As such, the use of heavy ion damage and deuterium as a proxy for neutrons and tritium in W allow for both more timely experiments and less specialization in radioactive materials. Most studies quantify damage with displacements per atom (dpa) when it is the concentration of trapping sites, i.e. traps per atom (tpa),  that is a better metric for determining retention.  In this work, we report our recent studies of deuterium retention in ITER-grade polycrystalline W before and after ion irradiation damage using D(3He,p)α nuclear reaction analysis (NRA) [2,3]. Multiple Cu ion beam energies (0.5, 2, and 5 MeV) were used to create a relatively uniform damage profile in W up to 1 micron depth at RT, with damage levels of 0.001, 0.01, and 0.1 dpa.  To isolate the effects of annealing, some of the irradiations were performed at elevated temperatures (300, 600, and 750 C). By exposing these samples to a low flux and low temperature D plasma, the near saturation of filled trapping sites effectively allows D to be used as a marker for traps in W via NRA. Results showed that increasing the level of damage decreases D retention in the damage region as well as reducing the amount of trapped D inventory beyond the damage region, while partial annealing during the irradiation before plasma exposure reduces D retention.

[1] W.R. Wampler and R.P. Doerner, Nucl. Fusion 49, 115023 (2009).
[2] J.L. Barton, et al., Nucl. Instr. Meth. B 332 (2014) 275-279.
[3] J.L. Barton, et al., J. Nucl. Mater., accepted and in press (2015).