Retention behaviour of deuterium and helium in beryllium under single D+ and dual He+/D+ exposure

Beryllium plates were irradiated with single deuterium and dual helium plus deuterium energetic ions with fluences of 1e17 ions/cm2 and 5e17 ions/cm2, and annealed afterwards in vacuum at 523, 723 and 923 K for 10 min. The surfaces were analysed with electron microscopy, X-ray diffraction and ion beam techniques. The results are consistent with well-established outcomes arising from helium irradiation, evidencing that the degassing mechanisms depend of the microstructure evolution. They point to a supersaturation of the implanted zone by helium in the samples exposed to fluences of 5e17 He+/cm2. In this case, it is observed a simultaneous release of helium and deuterium at lower temperatures, evidencing the formation of a porous microstructure from primary gas bubbles. In the absence of a porous structure, the helium degassing occurs at a higher temperature range, while it depends on the migration of helium-vacancy clusters. The supersaturation of beryllium was never reached under single deuterium irradiation, being the release of deuterium controlled by ion-induced trap sites.