Structure, morphology and deuterium retention and release properties of pure and mixed Be and W layers

Abstract

Deuterium retention and release behavior were investigated in this study, for beryllium, tungsten and mixed beryllium/tungsten thin layers which are of concern for next-generation thermonuclear fusion devices like International Thermonuclear Experimental Reactor. The layers prepared with thermionic vacuum arc technology by using two different ion acceleration voltages 0 V and −700 V respectively were subsequently implanted by exposure to a steady-state deuterium plasma with ion energies of 240 eV/D for D 3 and 360 eV/D for D 2 at a specific fluency of 2.85 × 10 20 m −2 s. Morphology is strongly influenced by layer composition and by the ion acceleration voltage applied in-situ during layer deposition. Crystalline structure analysis shows the presence of a polycrystalline W metallic phase and also highlights a dependence between tungsten crystallite size and Be/W atomic ratio. The amount of deuterium in mixed layers is lower than in pure beryllium layers indicating that W is mitigating D binding states. Results extrapolated for a 'cold chamber and divertor scenario' indicate a limited desorption efficiency (~20%), if the wall baking scenario, for tritium removal procedure in ITER, is to be applied to the investigated layers.

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.…”

“…To extrapolate useful results for ITER, more studies are needed to accurately predict the trapping and thermal release behavior of D from mixed Be-W layers. In this manuscript we continue our previous work in Dinca et al [36] by studying Be-W layers with the same metallic composition (Be-W (1:2, 1:1 and 2:1) as well as reference Be and W layers. Still, in this experiment the layers will be co-deposited with D, unlike the previous one where they were implanted.…”

“…However, this hypothesis cannot be verified using cross section images, due to work restrictions for beryllium. In a previous study [36] it was observed that a dense microstructure leads to a reduced D trapping in high energy binding states. Similar morphologies were observed for the rest of the mixed layers (Figure 2b,c), which can lead to the conclusion that in this case layer morphology is independent of Be and W composition.…”

“…During TDS measurements, the release of multiple gaseous species from the sample was monitored with an emphasis on mass 3 and mass 4, corresponding to HD and D2, respectively. As was observed in an earlier study [41], the release of D atoms from the codeposited samples was mainly dominated by D2, unlike the HD dominated release from implanted layers [36]. To quantify the D2 release, calibrations were performed by leaking known amounts of D2 into the TDS chamber.…”

Deuterium retention in mixed Be-W-D codeposited layers

“…Currently, very little is known about the effect of W presence in Be layers. Dinca et al [20], Jepu et al [21], Mateus et al [22], and Sugiyama et al [23] studied D implantation into deposited Be-W layers. However, D incorporation in a layer during its growth (codeposition) can differ considerably from D implantation into a deposited layer.…”