Impact of helium ion implantation on deuterium plasma induced microstructure evolution and deuterium retention in tungsten

Surface blistering and internal microstructure evolutions as well as deuterium retention in tungsten with helium ion implanted followed by deuterium plasma exposure were investigated. The helium ion implantation was taken with 40 keV with a flux of 1.6 × 10¹⁷ He⁺/(m²s) to a fluence of 6.0 × 10²⁰ He⁺/m² at room temperature. The following deuterium plasma exposure was taken with a flux of 5.96 × 10¹⁹ D/(m²s) at a bias of 100 eV at 340 K. The deuterium plasma exposure was designed with two different durations. One is about 19 h (h) which corresponds a fluence of 4.07 × 10²⁴ D/m², while another is nearly 96 h corresponds a fluence of 2.06 × 10²⁵ D/m². The helium ion implantation itself did not induce surface blister nor detectable internal helium bubble. After subsequent deuterium exposure of 19 h, dense surface blisters appeared on the reference tungsten, while no blister was formed on the helium implanted tungsten, indicating the helium ion implantation can efficiently suppress the surface blistering. However, when the deuterium irradiation time was increased up to 96 h, sparse deuterium blisters appeared on the surface of the helium ion pre-implanted W, indicating D could pass through the helium implantation layer as the exposure time was long enough. TEM results revealed that no bubble can be observed in the reference tungsten only exposed to deuterium plasma, while bubbles can be confirmed in the helium ion pre-implanted tungsten after deuterium irradiation, suggesting that the growth of helium bubbles can be enhanced by the subsequent deuterium plasma exposure. For the deuterium plasma exposure with 19 h, the total deuterium retention in the helium ion pre-implanted tungsten was three times that of the reference tungsten, indicating the helium ion implantation could increase the deuterium retention in tungsten.