Doppler broadening spectroscopy in the positron annihilation technique (DBS-PA) has been employed to investigate the defect properties in argon-damaged tungsten exposed to low-energy and high flux deuterium plasma. Argon ion irradiations with energy 500 keV are performed for tungsten samples with various levels of damage. The remarkable increment of the S parameter in DBS-PA indicates the introduction of vacancy-type defects in argon irradiated tungsten. An increase of ion fluence results in a continuous increase of the S parameter until saturation. Unexpectedly, a much higher fluence leads to a decrease of the S parameter in the near surface, and the (S,W) slope changes greatly. This should be associated with the formation of argon-vacancy complexes in the near surface produced by the excessive implanted argon ions. With deuterium plasma exposure, a significant decrease of the S parameter occurs in the pre-irradiated tungsten, suggesting the sharp reduction of the number and density of the vacancy-type defects. The thermal desorption spectroscopy results demonstrate that the argon-damaged tungsten, compared to the pristine one, exhibits an enhanced low-temperature desorption peak and an additional and broad high-temperature desorption peak, which indicates that deuterium atoms are trapped in both low-energy and high-energy sites. All these observations directly indicate the deuterium occupation of irradiation-induced vacancy defects in damaged tungsten, which is responsible for the remarkable increase of the deuterium retention in comparison with the pristine one.

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Effects of iron ion pre-irradiation with energy of 1 MeV on deuterium retention and blistering in tungsten has been investigated after exposure to low-energy (40 eV) and high flux (~1022 D m−2 s−1) deuterium plasma under high fluence of 1  ×  1026 D m−2 with various surface temperatures (450 K, 550 K and 750 K). The undamaged and pre-damaged tungsten show a similar temperature dependence of deuterium-induced blistering, as well as deuterium retention in the near surface (within 300 nm). Deuterium concentration in the near surface decreases with increasing the surface temperature in deuterium plasma exposure. For both cases, the most serious blistering is present at the surface temperature of 550 K. Due to the creation of pre-damage the size of surface blister becomes much larger and the near-surface deuterium concentration becomes higher. Analysis of blistering-related cavities in the pre-damaged and undamaged tungsten indicates that in pre-damaged tungsten deuterium aggregates in the place with a much larger depth. Based on the comparison of the pre-damage induced increment of deuterium retention within the near surface region (damage layer) and in the bulk, it reveals that the pre-damage enhances deuterium retention in the bulk more strongly than that in the near-surface region, suggesting that the deuterium flux diffusing into the bulk of pre-damaged tungsten is largely improved.

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