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

Abstract

The effect of deuterium (D) presence on the amount of displacement damage created in tungsten (W) during high-energy W-ion irradiation is investigated. For this purpose, we have performed modelling of experimental results where W was sequentially or simultaneously irradiated by 10.8 MeV W ions and exposed to 300 eV D ions. A novel displacement damage creation and stabilization model was newly developed and introduced into the MHIMS-Reservoir (Migration of Hydrogen Isotopes in MaterialS) code. It employs macroscopic rate equations (MREs) for solving the evolution of solute and trapped D concentrations in the material. The new displacement damage creation and stabilization model is based on spontaneous recombination of Frenkel pairs and stabilization of defects that are occupied by D atoms. By using the new model, we could successfully replicate the measured D depth profiles and D thermal desorption data, where a higher defect concentration was observed when D was present during W irradiation as compared to when no D was present. For this we utilized parameters, which include the number of distinct defect types, the de-trapping energies of their fill-levels, their saturation concentrations and their probability for stabilization if they contain a D during the W-ion irradiation. To successfully replicate the experimental results three distinct defect types were needed with several fill-levels. By comparing the de-trapping energies of the defect filllevels with data available from the literature, the defect types were identified as single-vacancies, small vacancy clusters and large vacancy clusters. The effect of D presence was found to be largest in single vacancies as its concentration increased by about a factor of three, while the concentration of small vacancy clusters increased by about a factor of two. Large vacancy clusters were found to be largely unaffected as they showed very little increase in concentration when D was present.

Deuterium transport and retention in the bulk of tungsten containing helium: the effect of helium concentration and microstructure

“…This was to the author's knowledge never experimentally observed before and means that He differently influences on HI trapping as compared to the only W irradiated and hence displacement damaged W. In the latter case it is typically observed that a diffusion front with constant D concentration is moving deeper into the sample. The simulation of the data from figure 9 showed us that we were able to get a good agreement with the experimental D depth profiles and D desorption spectrum only when the de-trapping energy in the He zone was set slightly lower (1.74 eV) as compared to the de-trapping energy for the traps due to W ion irradiation (1.82 and 2.06 eV, figure 14) which we assume are vacancy clusters and voids [63].…”

“…The obtained D concentrations for the plasma exposures are higher as compared to the D atom exposures. This is attributed to the lower exposure temperature (450-470 K) and higher D ion flux for the plasma experiments, where traps with lower de-trapping energy can be populated [63], which is not the case for D atom exposure at 600 K. Still we observe similar, almost linear decrease of D concentration at high annealing temperature of 1700 K, as was observed in a recent study by Zibrov et al [51]. For the 'He' side no decrease in D concentration is observed after annealing to 1700 K. We observe even an increase by 20 %, which is due to accumulation of He at high temperatures.…”

Effect of D on the evolution of radiation damage in W during high temperature annealing

“…At an annealing temperature of 600 K about 30 % of its reference density is lost and at 800 K, approximately 50 % of the reference amount is annealed. In our previous publication [18] this defect was inferred to be single vacancies. Defect type II, that desorbs in the high-temperature D desorption peak centered at 780 K, shows no reduction in density for temperatures lower or equal to 600 K, while at 800 K around 33 % of reference defect density is annealed.…”

“…Defect type II was inferred to be small vacancy clusters in Ref. [18]. Defect type III shows no behaviour with rising annealing temperature.…”

“…In other cases, the D retention measured by TDS is approximately 10 % less than the D retention measured by NRA, which coincidentally compensates the 10 % simulation overestimation because of the low temperature D desorption early rise. This rise is an unexplained but common occurrence when the simulated D desorption spectra are compared to experimental spectra [18], [25], [28],…”