Annealing of He-related defects and their influence on deuterium retention in displacement-damaged EUROFER97

Abstract

This work investigates the thermal evolution of He-related defects and their impact on deuterium (D) retention in EUROFER97. Samples were irradiated at 290 K with 20 MeV tungsten (W) ions to a primary peak damage dose of 0.6 dpa followed by 0.5 MeV He ions to a peak concentration of 0.6 at.% to mimic the aspects of fusion neutron damage. These samples were then exposed to a low-temperature D plasma to fill the radiation-induced defects with D. Nuclear reaction analysis with ${}^3$He (${}^3$He-NRA) was applied to determine the depth profiles of the retained D. Thermal desorption spectroscopy (TDS) was employed to investigate D desorption. The experimental cycle of D-loading/NRA/TDS was systematically repeated, and the maximum TDS temperature was increased by 50 K in each step (from 420 K up to 720 K). This allowed studying the thermal evolution of the D trapping sites. Although the density of He-related traps decreases monotonically with increasing temperature, they are not completely recovered even after annealing at 720 K. It was concluded that the presence of He bubbles, which were observed by transmission electron microscopy (TEM), significantly increases the local D concentration. The simulation of TDS spectra utilizing a macroscopic rate equation code (TESSIM-X) reveals a D detrapping energy from He-related defects of 1.00 eV.