Helium thermal desorption and retention properties of V–4Cr–4Ti alloy used for first wall of breeding blanket

Helium irradiation experiments of V–4Cr–4Ti alloy with various surface treatments were conducted in an electron cyclotron resonance (ECR) ion irradiation apparatus. After helium ion irradiation at room temperature, the helium thermal desorption and retention properties were examined by thermal desorption spectroscopy (TDS). Ion energy of helium beam was 5 keV. Three groups of desorption peaks appeared at around 500, 850 and 1200 K in the TDS spectrum. After helium ion irradiation at ion fluence of 1 × 1021 He/m2, the retained helium desorbed mainly at around 1200 K and all of the implanted helium atoms were retained. With increasing fluence up to 5 × 1021 He/m2, the amount of helium desorbed at 500 K increased. For the polished samples with annealing at various temperatures, the desorption peak observed at around 500 K shifted to higher temperature region. Smallest retained amount of helium was observed in the V-alloy with polishing followed by annealing at 1373 K.