Deuterium retention in tungsten for fusion use

The retention of deuterium in polycrystalline W foils has been measured as a function of ion fluence and implantation temperature. At temperatures in the range 350-550 K, retention levels were found to be above the 300 K value. This retention enhancement is attributed to an increase in the D diffusion coefficient, which allows a greater diffusion depth. Furthermore, while retention at room temperature saturates as a function of fluence, at 500 K no saturation is observed. D(3He,4He)p nuclear reaction analysis measurements show that at room temperature most of the D is trapped in the near-surface region of the specimen, but significantly beyond the implantation range. At higher temperatures, much lower levels are observed in the near-surface, and diffusion through to the back of thin specimens is observed: the front and back surface D concentrations are similar. While the D retention in a proposed W alloy for ITER applications (W-1%La2O3) is similar to that measured in the pure W foils over most of the range of the experiments, two important differences are noted: a trend to saturation of the amount retained is observed at fluences >1024 D/m2 and 500 K, and the D concentration at the back of the W-1%La2O3 alloy is about 1% of that at the implanted surface. (orig.)