Release of ion-implanted 3He and D from tungsten under subsequent 4He ion irradiation

The efficiency of deuterium (D) and ³He atoms removal from polycrystalline tungsten (W) by irradiation with 3 keV ⁴He ions at room temperature was investigated. It was shown that up to 90% of He isotopes are replaced by post-irradiation with another He isotopes in both directions when saturation with He atoms in W is achieved. There are at least four processes of He isotope exchange and D-He exchange, namely, (1) collision, (2) sputtering, (3) bubble bursting and (4) replacement of previously trapped atom by post-implanted atom. It was shown that the sputtering and bubble bursting play a minor role in the removal of D and He by 3 keV ⁴He ions in comparison with collision and replacement processes. In the case of He isotope exchange, the dominate process is most likely a replacement. Replacement occurs even at room temperature regardless on the binding energy of He with defects, probably, by decreasing of the binding energy of He or D atoms with defects when He atoms during sequential irradiation approach them. In the case of D-He exchange, both collision cascade and replacement play a main role in the D removal by 3 keV ⁴He ions. The mechanism of the D and He removal by He ions is still need further study.