Characteristic changes of deuterium retention on tungsten surfaces due to low-energy helium plasma pre-exposure

Deuterium retention in tungsten increases substantially when it is pre-exposed to low-energy He plasma at a high temperature (1600 K), while it decreases when pre-exposed at a low temperature (700 K). The increase of deuterium retention could be attributed to the submicron-sized He bubbles and secondary interstitial defects formed on the tungsten surface. Occupation of trap sites by He atoms during the He pre-exposure at low temperature could decreases the effective number of available trap sites for deuterium atoms, which would decreases the deuterium retention on the tungsten surface.