Displacement damage stabilization by hydrogen presence under simultaneous W ion damage and D ion exposure

Abstract

Polycrystalline tungsten (W) samples were simultaneously irradiated by 10.8 MeV W ions and exposed to 300 eV deuterium (D) ions at different temperatures ranging from 450 K to 1000 K. After the simultaneous W ion irradiation and D ion exposure the samples were additionally exposed to low energy D ions at 450 K in order to populate all the defects created beforehand. The amount of damage created was evaluated by measuring D depth profiles and D thermal desorption spectra. Results are compared with data obtained in a sequential experiment where samples were first irradiated by 10.8 MeV W ions and only afterwards exposed to 300 eV D ions at 450 K to populate the created defects. At 450 K we observe a two times higher maximum D concentration for the simultaneous case as compared with the sequential case. At 600 K and 800 K the ratio between simultaneous and sequential decreases to about 1.6 and 1.2, respectively, and increases again to a factor of two at 1000 K. We attribute this dependence on temperature to the change in the concentration of mobile and trapped D during the simultaneous exposures, which is in line with theoretical calculations predicting that trapped D in a vacancy prevents vacancy annihilation with self-interstitials.

New rate equation model to describe the stabilization of displacement damage by hydrogen atoms during ion irradiation in tungsten

“…They have found detrapping energies ranging from 0.8 -1.2 eV for various dislocation structures, number of trapped HIs and for various number of trapped self-interstitial W atoms. Although some of these de-trapping energies are in line with our defect type II fill-level de-trapping energies the typical dislocation areal density found in such samples by TEM analysis [27,53] is around 10 14 m -2 . This is equivalent to a volumetric concentration of 10 -4 at.%.…”

“…6. The D flux at the position where these D depth profiles were measured was determined to be 𝛤 𝐷 = 1.3 × 10 18 D m -2 s -1 [27]. The fall in D concentrations with rising irradiation temperature that is observed in the experiment is described well by the simulation owing its success mainly to the correct choice of parameters of stabilization α and the de-trapping energies.…”

“…To simulate the sequential W-D and the simultaneous W/D-D experimental results [27] we used a variant of the MHIMS (Migration of Hydrogen Isotopes in MaterialS) code [11]. The code is based on a 1D rate equation model which is used to simulate D depth distributions and D desorption spectra in experiments where HI retention and transport mechanisms are of interest.…”

“…In this paper we model the results of a succeeding experimental study where W samples were irradiated with 10.8 MeV W ions to a displacement damage dose of 0.35 dpa at various temperatures and exposed to 300 eV/D ions instead of atoms up to a fluence of 2.8 × 10 23 D m -2 [27]. To describe this new experiment, we have used and upgraded the MRE model in the MHIMS-R code so it is able to describe the process of displacement damage creation by energetic heavy ions with or without the presence of D [26].…”

Recent advances in characterising irradiation damage in tungsten for fusion power

“…Interestingly a recent study shows that the deuterium retention will be even higher when simultaneous implantations are performed as may happen in-service during the reactor operation. Markelj et al [114] compared deuterium retention in tungsten samples sequentially implanted with tungsten ions and deuterium with the retention in tungsten simultaneously implanted with deuterium and tungsten ions. Examining a range of temperature, Markelj et al [114] concludes that between 300 and 1000 K, deuterium retention in simultaneously implanted samples is almost a factor of two higher than in the sequentially implanted case.…”