Effect of helium irradiation on trapping and thermal release of deuterium implanted in tungsten

Retention and thermal release of D atoms and lattice disorder in W single crystals pre-irradiated with He were studied by ion beam analysis techniques. The retention of 1 keV D ions implanted in W crystals was strongly enhanced by the 10 keV 4He pre-irradiation to a small dose where a large distortion was created at room temperature. The total amount of D retained in near surface layer of the W crystal did not vary with a range of He pre-implantation dose between 1019 He/m2 and 1021 He/m2. However, the lattice disorder was significantly accumulated in near surface layer above 1021 He/m2 and the thermal release of retained D atoms occurred at higher temperature. For a specimen pre-irradiated at 850 K, the crystal lattice was not heavily damaged, and trapping sites for the D atoms were uniformly distributed in the He implanted region probably owing to ordered He bubbles.