Study of H⁺ irradiation induced vacancy-type defects in RAFM steel by slow positron beams

[Background] RAFM steel is a good candidate structural material and is widely accepted today as a fusion reactor core material. [Purpose] This study aims to investigate the radiation damage mechanism of reduced activation ferritic/martensitic (RAFM) steel, the vacancy-type defects and their effects on the material structure of RAFM steel irradiated by H⁺ were probed by slow positron beam. [Methods] The experimental sample was RAFM steel based on Fe-9 wt.% Cr. H⁺ ion beam energy was 100 keV whilst the dose was set to be 1 × 10¹⁵ cm^-2, 1 × 10¹⁶ cm^-2, 1 × 10¹⁷ cm^-2, respectively, for irradiation experiments. [Results] The results of slow positron beam Doppler broadening measurement were available. The S parameter increased with the increase of dose, and the W parameter shows the opposite trend. The main irradiation area of the material was 142 ∼ 348 nm, there were a large number of defects in this range, the irradiation mainly produced vacancy-type defects, most of which were hydrogen-vacancy complex defects. The concentration of irradiation defects increased with the H⁺ doses. [Conclusions] The size of the vacancy-type defect changes with the dose increase. When the irradiation dose reaches 10¹⁷ cm^-2, the slope of the S-W curve changed, so the type of irradiation defects varies significantly, and the defects of larger size were occurred. (authors)