Reduced deuterium retention in self-damaged tungsten exposed to high-flux plasmas at high surface temperatures

Abstract

We investigated the effect of surface temperature on deuterium retention in self-damaged tungsten exposed to high-flux deuterium plasmas. The retention saturates at a W 4+ fluence of about 3 × 10 17 m −2 and is strongly reduced for the present high surface temperatures of 800-1200 K as compared to previous experiments at 470-525 K. Combination of nuclear reaction analysis (NRA), thermal desorption spectroscopy and positron annihilation Doppler broadening (PADB) was used to investigate the reduction in deuterium retention. The NRA showed a strong reduction of retention at the surface at high surface temperatures. The PADB measurements suggest that during plasma exposure defects are mobile and cluster into larger clusters containing up to a few tens of vacancies. Tritium Migration Analysis Program 7 simulations show that trapping and de-trapping rates are very high for defects with trapping energies below ∼1.5 eV. The strong reduction in retention seems to be caused by the reduced amount of mono-vacancies and small vacancy clusters in combination with their strong depopulation due to thermal trapping and de-trapping.

Deuterium retention and surface modifications of nanocrystalline tungsten films exposed to high-flux plasma

“…These blisters are similar to the ones described in Ref. [7], and probably originate from plastic deformation. On columnar coatings many more and larger blisters are observed (Fig.…”

“…These nanostructures resemble the formations discussed in Ref. [7]. Xu et al characterized such structures and found that their appearance is dependent on the grain orientation [8].…”

Deuterium trapping at defects created with neutron and ion irradiations in tungsten

“…In addition, Edet decreases with increase in the number of D atoms trapped in a mono-vacancy [21,22]. This is one of the reasons for the broad desorption peak observed after the exposure at 473 K. Indeed, 't Hoen et al [23] performed positron annihilation Doppler broadening and D retention measurements for W specimen irradiated with 12.3MeV W ions and reported that clustering of vacancies took place at 650 K. They observed reduction in D retention with increase in the exposure temperature and explained this observation by the reduced amount of mono-vacancies and small vacancy clusters in combination with the strong depopulation with D due to thermal trapping and detrapping [23]. In any case, an improvement of modelling such as TMAP is necessary to analyse the desorption spectra acquired under the conditions where annealing of defects is significant.…”

Strongly Reduced Penetration of Atomic Deuterium in Radiation-Damaged Tungsten

“…The program includes trapping of deuterium and recombination to molecules at the surface. Following our previous results [9], we assume three different trap sites for deuterium in tungsten with trap densities of 2 Â 10 À1 , 4:5 Â 10 À1 , and 6:5 Â 10 À1 at. % for trapping energies of 1.2, 1.4, and 1.85 eV, respectively.…”

“…The surface cleanliness was checked by x-ray photoelectron spectroscopy. Since the targets were PRL 111, 225001 (2013) P H Y S I C A L R E V I E W L E T T E R S week ending 27 NOVEMBER 2013 stored under ambient conditions, they were covered with nanometer-thick native layers of oxygen and carbon [3,9]. During plasma exposure, most of these layers are removed within the first few seconds, although the presence of in particular some oxygen cannot be excluded [10].…”