Cluster dynamics modeling of hydrogen saturation retention in tungsten with a universal trapping-site sink strength

TL;DR

This paper introduces a universal trapping-site sink strength model integrated into cluster dynamics to accurately simulate hydrogen retention saturation in tungsten, aligning well with experimental data and revealing microstructural effects.

Contribution

A novel dynamic trapping-site model that accounts for saturation effects in hydrogen retention, improving upon existing sink strength models for tungsten under irradiation.

Findings

Quantitative reproduction of hydrogen retention saturation in tungsten.

Identification of a critical fluence threshold (~10^23 m^-2) for saturation.

Microstructural effects on hydrogen trapping are quantitatively characterized.

Abstract

Hydrogen isotope (HI) retention poses a key issue for tungsten (W)-based plasma-facing materials (PFMs) in fusion devices, where microstructures such as dislocations (DLs) and grain boundaries (GBs) play a dominant role. Existing theoretical sink strength models for microstructures like DLs and GBs fail to account for the observed saturation of HI retention. In this study, we propose a novel universal trapping-site model that dynamically represents sink strengths as time-dependent site concentrations, which is incorporated into an improved cluster dynamics model for high-fluence HI irradiation. Our simulations quantitatively reproduce the saturated low-energy deuterium (D) retention and depth profiles in W, in good agreement with experiments. A critical saturation fluence of approximately 1023 m-2 is identified, below which unsaturated D retention is governed by both GBs and ion-induced defects, whereas above this threshold GBs dominate D retention by trapping free D and approaching their theoretical saturation limit. The trapping-site sink strength model enables quantification of H trapping by diverse microstructures via unified effective site concentrations, providing mechanistic insights into microstructural effects and facilitating direct evaluation of HI retention in PFMs under different irradiation conditions.