Hydrogen-vacancy interaction in tungsten

Abstract

Hydrogen-vacancy interaction in tungsten was investigated by means of the perturbed angular correlation technique, using the isotope '"In as a probe.Hydrogen trapping at an "'In-vacancy cluster manifests itself as a change of the locd electric field gradient, which gives rise to an observable shift of the quadrupole frequency. The measurements show that a vacancy in tungsten can trap one or two hydrogen a t o m at room temperature. The detrapping energies of the first and second hydrogen atom are 1.55(2) and 1.38(2) eV, mpectively, while the detrapping enof the next hydrogen atom is less than 1.1 eV. Substitutional " ' I n atoms do not trap hydrogen at room temperature. At least two more hydmga decorated defects were observed. Although their StmctureS are not quite clear, they probably fonn from larger vacancy clusters and may eontain a large amount of hydrogen. The dissociation energy of these bubble-like defects is 1.30(2) eV.

Plasma-material interactions in current tokamaks and their implications for next step fusion reactors

“…The concentration profile is also shown for two cases: (1) with a high near-surface concentration resulting from a sluggish re-emission from the surface, and (2) with a lower near-surface concentration resulting from an enhanced re-emission of implanted flux to the plasma. This, in turn, means a reduced driving potential for diffusion into the bulk; (figure provided by G. [403], activation energy for diffusion E m =0.39 eV [403], binding enthalpy of hydrogen to a vacancy Q t =1.1 eV [400,401], enthalpy of adsorption Q a =0.7 eV [404,405] 39 Net carbon erosion rate at the divertor strike-point vs. strike-point heat flux on JET and DIII-D. JET data [110] and DiMES at 1.5 MW·m −2 [521] were obtained with colorimetry. All other DiMES data come from depthmarked insertable probes [480,530].…”

“…[376,[399][400][401][402] appear at the bottom of Trapping of hydrogen at helium bubbles produced by implantation of helium into metals has also been studied extensively. This is relevant to fusion plasma environments where helium bubbles may be formed by implantation of fusion alpha particles, by tritium decay or by neutron-induced transmutation, e.g., in materials like beryllium.…”

“…However, in Be with higher oxygen and carbon content, the concentration of retained D is relatively higher and approaches that of carbon. (b) Perturbed angular correlation [401] (c) [399] (d) Density functional theory [402] Sources for values not referenced here are given in Ref. [376].…”

Deuterium inventory in the full-tungsten divertor of ASDEX Upgrade

“…Recent laboratory investigations suggested different trapping sites in PC-W, i.e. (1) weak trapping in dislocations / grain boundaries with a trapping energy: E trap of 0.6 -0.9 eV, (2) trapping in vacancies / bubbles with E trap ~ 1.2 -1.6 eV and (3) chemisorption on the inner surface of a void with a high trapping energy (E trap ~ 1.8 -2.0 eV) [22,23,[26][27][28]. In the case of PC-W, D is mainly trapped in (1) and (2) sites under RT irradiation, while trapping by (3) sites becomes dominant under higher temperature irradiation conditions.…”

The Depths of Hydrogen and Helium Bubbles in Tungsten: A Comparison

“…In order to fully account for this type of event, the binding energy of multiple filled traps as a function of occupancy would have to be known. This type of datum exists for small clusters, consisting of 1 to 2 hydrogen atoms in a vacancy 75 ; but without some growth mechanism that actually increases the size of the cavity~from one vacancy!, these clusters cannot account for the large bubbles. In the literature there are reports of traps with energies between 0.5 eV~"natural traps" in unirradiated single-crystalline tungsten 32 !…”