Tungsten fuzz annealing effect on deuterium retention in polycrystalline tungsten

Using a beam-plasma discharge device operating on helium (He), tungsten with the fuzz on the surface (Wf) has been formed by irradiating polycrystalline tungsten (W) samples with He ions with an energy of ∼150 eV and the fluence of ∼6 × 1024 He/m2 at the temperature of 1273 K. The deuterium (D) retention in Wf annealed at different temperatures was studied by thermal desorption spectroscopy (TDS). Before and after annealing at temperatures of 1000,1200,1400 and 1600 K, Wf was irradiated at room temperature by 2 keV D3+(667 eV/D) ions with the fluence of 1021 D/m2, then in-situ TDS was performed after each irradiation. Annealing W above 1200 K clearly changes the retention mechanism of D: the TDS spectrum consisting of multiple peaks changes to an almost single-peak spectrum. Annealing at 1600 K leads to surface smoothing and the decrease of the D retention by a factor of two compared to the annealing at 1000 K. This can be explained by an increase of the reflection coefficient for the flat W surface. However, the D retention in Wf is significantly higher compared to that in W without He plasma exposure even after annealing at 1600 K, because there are still He bubbles in Wf that effectively trap D