Temperature-dependent bubble growth under synergistic interactions of hydrogen and helium in tungsten

A novel theoretical model based on modified diffusion rate equations is proposed to simulate the retention of hydrogen isotopes and the dynamics of bubble growth in tungsten (W) when exposed to simultaneous hydrogen (H) and helium (He) plasma irradiations. Simulation is conducted to assess the influence of temperature as well as simultaneous H and He irradiation at an increasing fluence. Not only to develop a holistic understanding but also to substantiate simulation findings about synergy between H and He plasma irradiation, a W sample is exposed sequentially to H and He plasma at 873 K using the large-power material irradiation experimental system. The topographical changes in the W sample are investigated using atomic force microscopy (AFM) after each plasma irradiation exposure sequence. Simulation results reveal that the ability of a bubble containing both H and He to trap adjacent H/He atoms is primarily governed by their individual partial pressure within the bubble. Furthermore, at elevated temperatures, the synergy between H and He significantly enhances the retention of H isotopes in W. AFM micrographs of the W sample exposed to both H and He plasma irradiation show a severely damaged and locally delaminated layer, absent in the sample exposed only to either H or He, conclusively establishing evidence of synergy between H and He irradiation effects. The average bubble radius computed using the model aligns excellently with experimentally determined values obtained through SEM/AFM analysis. The robustness of the proposed model is also assessed by comparing bubble radius and H isotopes retention at various temperatures with experimental data reported in the literature.