Deuterium retention in mixed Be-W-D codeposited layers

Abstract

Mixed beryllium-tungsten-deuterium (Be-W-D) layers (4.4-28.4 at.% W) were codeposited in a magnetron discharge in D 2 -Ar atmosphere at pressures of 0.8 Pa, 2.7 Pa, and 8 Pa and a substrate temperature of 373 ± 15 K. The composition of the layers was determined using nuclear reaction analysis and Rutherford backscattering spectrometry. D trapping states in the layers were examined using thermal desorption spectroscopy. At all pressures used, the D concentration in the layers has a nonmonotonic dependence on the W concentration, with the maximum occurring at 4.4-7.3% W. In this case, the D concentration is about two times greater than that in a Be-D layer; in W-D layers the D concentration is more than one order of magnitude smaller. Increase of pressure during deposition results in an increase of the D concentration in Be-D and Be-W-D (4.4-7.3% W) layers and is linked with the appearance of sharp low-temperature D release peaks near 450 K and 500 K. Increase of pressure also results in steeper decrease of the D concentration with increasing W concentration beyond 7.3%. It is concluded that for the layers deposited at 450 K and above, the effect of the presence of W (4.4-28.4%) on the D retention becomes small.

Deuterium Retention in Mixed Layers with Application in Fusion Technology

“…BeD 2 formation was only observed for the W33 sample and one can argue that the high Be concentration in this sample is the main reason. However, a crystalline phase corresponding to BeD 2 was not observed for the Be layers presented in this study or in previous studies where the layers were produced using the direct current magnetron sputtering technique [36,38,41]. Thus, the formation of these compounds here is not clearly understood.…”

“…These two manuscripts can provide the basis for a comparison between the main D retention mechanisms in ITER (co-deposition and implantation) applied for a specific case. On the other hand, it can also be viewed as a continuation of Zibrov et al's [38] study and the results can bridge the gap in knowledge for a mixed Be-W layer with W content higher than 28%.…”

“…Among other structural and compositional differences, the authors observed that nitrogen significantly alters the trapping mechanisms and shifts the D desorption onset to higher temperatures, which could potentially affect the tritium removal procedures in ITER. It was also pointed out that N desorption is very well correlated with D desorption potentially acting as a trapping state barrier for D. This was followed by a more complex work by Zibrov et al over a wide range of samples deposited at 0.8, 2.7 and 8 Pa respectively, with small amounts of W impurities (4.3-28 at%) [38]. He observed that D retention is positively correlated with the increase of gas mixture pressure and, in contrast with the conclusions of K. Sugiyama et al [34], the results indicate an increase of retention with a factor of two for layers with low W content (4.3-7.3 at%) in comparison to Be-D layers, independently of the deposition pressure.…”

“…However, the above relation is extrapolated based on very few results and a narrow range of deposition pressures. To compare our results with the ones presented by Zibrov et al [38], the retention is converted in at% using the RBS results (which gives the density of Be and W atoms). It can be seen that, despite the different deposition pressure, the three sets of data follow the same trend, namely the D concentration in the samples decreases with W concentrations.…”

Deuterium Retention and Release Behavior from Beryllium Co-Deposited Layers at Distinct Ar/D Ratio

“…The results show that the operating pressure range in ITER could significantly affect the crystalline structure and deuterium amount retained in Be-D layers formed in the cooler (373 K) areas of the inner vessel [26].…”