Hydrogen atom-ion synergy in surface lattice modification at sub-threshold energy

The promotion effect of uniaxial strain on hydrogen aggregation in tungsten

“…For example, using density functional theory (DFT) data and thermodynamic models, Hodille et al (2018) and Middleburgh et al (2014) believed the oversaturation originates from the H-induced reduction of vacancy formation energy, which promotes the vacancy amount that may accommodate excessive H atoms. Meanwhile, Gao et al (2017), Gao et al (2020) and Kato et al (2015) claimed that high concentrations of pre-existing H prevent the recombination of vacancies with self-interstitial atoms, and thus significantly reduce the displacement threshold energy and facilitate vacancy formation in W. In addition to vacancies, dislocations (Terentyev et al, 2014; and grain boundaries (GBs) have also been considered to be main contributors to H retention, although H oversaturation has been widely observed in recrystallized and/or single crystal W with very low dislocations/GBs density (Alimov et al, 2005;Zibrov et al, 2017;Zhang et al, 2021). To complicate matters further, recent experiments demonstrated that super-saturated H retention is almost independent of pre-existing impurities and defects (Jia et al, 2017), suggesting that the evolution of H itself is of high importance for such oversaturation.…”

Modelling of hydrogen isotopes trapping, diffusion and permeation in divertor monoblocks under ITER-like conditions

“…Its thickness is e = 12 mm and its width is w = 28 mm. On the one hand, the ions from the plasma are implanted in the first nanometres in which specific trapping processes can occurs such as the formation of the super-saturated layer (SSL) [19,20]. On the other hand, the retention in such a complex component requires a 2D geometry especially when dealing with high surface temperatures [10].…”

“…This SSL is only formed in the implantation zone of the ions where the ions transfer their energy to the lattice. The explanation proposed in [24] and [20] is that the implantation zone is the only place where the kinetic barriers can be overcome to reach the thermodynamic equilibrium. According to the model described in [24], the SSL formation is conditioned upon the exposure conditions (temperature and incident flux of hydrogen).…”

“…This is calculated by the model with a volumetric implantation source (with MHIMS) and given as an input to FESTIM. However, one can estimate the concentration of mobile particles for a given set of exposure conditions assuming no (or negligible) gradient to the bulk and a full recycling of implanted D [11,20,24]:…”

“…Super-saturated layer We modelled a SSL in the sub-surface by a fixed concentration of monovacancies up to 10 nm. However, such a SSL is induced by D ion irradiations [19,20] and one should include the dynamics of defect formation in the model using trap creation equation as proposed in [49,50]. Such model exists in MHIMS [6,51] and have even been upgraded to account for the stabilisation of traps by the presence of trapped H [52,53].…”