M. Poon

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( 3 He, 4 He)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%La 2 O 3 ) 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 >10 24 D/m 2 and 500 K, and the D concentration at the back of the W-1%La 2 O 3 alloy is about 1% of that at the implanted surface.

Deuterium retention in single crystal tungsten

Abstract The retention of deuterium in single crystal tungsten (SCW) has been measured at 300 and 500 K, as a function of incident ion fluence over the range 10 21 –10 24 D + / m 2 . Irradiation of SCW with 1.5 keV D 3 + ions at 300 K leads to saturation at a much lower incident fluence than seen in polycrystalline tungsten (PCW), but with the same levels of D retention at saturation, ≈5×10 20 D / m 2 . Implantations at 500 K reached saturation at a very low incident fluence, below 10 21 D + / m 2 , with the amount of D retained at saturation ≈1.5×10 20 D / m 2 . This level is 3–4 times lower than the saturation value for 300 K implantation of the same single crystal of tungsten. Deuterium depth profile analysis by secondary ion mass spectrometry (SIMS) shows D trapping primarily within the 500 eV D + ion implantation range for both 300 and 500 K profiles. SIMS also revealed that the depth profiles for oxygen and deuterium were similar. When the tungsten was annealed at 500 K for 1 h after implantation at 500 K, SIMS indicated that the deuterium retention decreased by an order of magnitude.

An Interpretation Of The Retention Of Low Energy Deuterium Ions In Tungsten

This report is a summary of our investigations of D retention in various forms of tungsten: high purity polycrystalline W (PCW), polycrystalline W containing 1% La2O3, and two grades of single crystal W (SCW). The experiments have been primarily implantations followed by thermal desorption measurements. Nuclear reaction analysis and SIMS were used to measure the depth distributions near the surface. By using low energy ions (500 eV/D+), it has been possible to eliminate most if not all elastic collision defect creation, yet this has not reduced the trapping significantly. Comparing the results for the various forms of W has enabled us to assess the effects of grain boundaries, dislocations and impurities. Recent work has included a study of the effects of ion flux on deuterium retention in SCW. The conclusion drawn is that D is trapped in clusters or nano-bubbles, and that these traps grow with increasing fluence, particularly at higher temperatures. The large variations in the retention of D in W show that the processes controlling D trapping are many and complex. In order to form a more comprehensive picture, and eventually attempt to predict retention under fusion relevant conditions, modeling has been performed using TMAP4[1].