Depth synergistic effect of irradiation damage on tungsten irradiated by He-ions with various energies

To simulate the uniform depth-distribution of damages introduced by neutrons, He-ions irradiations with different energies were respectively (W-1@16 keV, W-2@70 keV, W-3@200 keV) or successively (W-4@200-70-16 keV) conducted on the recrystallized tungsten. The damage defect distribution and helium behavior in tungsten were investigated by Positron Annihilation Spectroscopy (PAS). Results show that a sufficient number of small-size vacancy clusters containing low ratio of He atoms are produced in tungsten during a single-energy He-ions irradiation with a fluence below 1021 ions m−2 at room temperature (RT). But more irradiation dose will promote the saturation of the interstitial helium around the positron annihilation sites and accelerate the formation of helium-vacancy clusters. The fitted S profile of W-4 presents a platform in the depth range of 27–477 nm. Meanwhile, S-W line of it deviates from the line of W-1, 2 to W-3, and the (S, W) data form clusters in the depth range of 57–230 nm. These changes may be explained by a large quantity captures of injected He ions in defect sites and the formation of large-size HenVm clusters with continuously increasing n/m ratio. Fortunately, successive He-ions irradiation with various energies can, to some extent, achieve a quasi-uniform damage distribution in a certain depth range in metals, which meets the expectation in this paper.