Modeling spatially dependent kinetics of helium desorption in BCC iron following He ion implantation

One of the most important tasks in fusion materials research is to study the effect of helium on the microstructure and mechanical property evolution of structural materials. Thermal helium desorption spectrometry (THDS), through measuring the outward He surface flux as a function of temperature (or time), provides indirect information about the kinetics and energetics of helium transport and trapping/detrapping which is important for developing a predictive assessment for the life performance of fusion reactors. Nevertheless, THDS data interpretation is not straightforward, particularly when a broad temperature regime and a high He concentration are concerned. Here we present results from a spatially-dependent rate theory modeling framework in coordination with our previous THDS experiments on single crystal iron implanted with 4He+ ions at 5 or 10 keV to fluences of 1018 or 1019 He/m2. The model incorporates both temporally and spatially dependent diffusion, trapping, and detrapping (emission) kinetics for both implantation process and post-implantation thermal annealing. Possible desorption sequences/mechanisms are discussed.