Influence of exposure conditions on helium transport and bubble growth in tungsten

Helium diffusion, clustering and bubble nucleation and growth is modelled using the finite element method. The existing model from Faney et al. (Model Simul Mater Sci Eng 22:065010, 2018; Nucl Fusion 55:013014, 2015) is implemented with FEniCS and simplified in order to greatly reduce the number of equations. A parametric study is performed to investigate the influence of exposure conditions on helium inventory, bubbles density and size. Temperature is varied from 120 K to 1200 K and the implanted flux of 100 eV He is varied from 1017 m−2 s−1 to 5 × 1021 m−2 s−1. Bubble mean size increases as a power law of time whereas the bubble density reaches a maximum. The maximum He content in bubbles was approximately 4 × 108 He at 5 × 1021 m−2 s−1. After 1 h of exposure, the helium inventory varies from 5 × 1016 m−2 at low flux and high temperature to 1025 m−2 at high flux and low temperature. The bubbles inventory varies from 5 × 1012 bubbles m−2 to 2 × 1019 bubbles m−2. Comparison with experimental measurements is performed. The bubble density simulated by the model is in quantitative agreement with experiments.