Modelling of deuterium diffusion and thermal desorption in tungsten exposed to high-flux deuterium plasma

In nuclear fusion, hydrogen isotopes transportation in tungsten has been identified as a crucial process which could affect various key processes in the operation of a fusion device, such as tritium self-sustaining and operational safety. To enhance the understanding of deuterium diffusion and trapping in millimeter-thick tungsten under high-flux plasma conditions, we carried out a systematic simulation investigation on the deuterium plasma exposure and subsequent thermal desorption using the TMAP7 code based on experimental results. The simulation reveals that the defect concentration with a low de-trapping energy , as estimated solely from simulating thermal desorption, is lower than its actual density due to the temperature history of plasma exposure and subsequent cooling processes. Moreover, the growth rate of deuterium mobile concentration exhibits nonmonotonic behavior over time during plasma exposure, which strongly depends on the ratio of defect concentration with a high de-trapping energy to that with a low de-trapping energy. Additionally, we observed that the maximum deuterium diffusion depth does not follow a proportional relationship with the square root of exposure time, which is attributed to the growing number of plasma-induced defects and the reducing injection coefficient with increasing fluences. This work provides valuable insights into the understanding of deuterium transportation in tungsten during high-flux plasma exposure which could contribute to understanding and modelling of hydrogen isotopes recycling in future fusion devices.