Review of hydrogen retention in tungsten

Although extensive studies on hydrogen (H) retention in tungsten (W) loaded by ion implantation, plasma exposure and gas charging have been done, reported amounts of H retained in W, and their dependences on the incident flux, fluence and temperature are very inconsistent. The present work aims at the clarification of the H retention mechanisms with critical review of reported data and presentation of recent results. H diffusion coefficient for dissolved H in W is large enough to allow for a deep penetration of H into W bulk. Energetic H loading results in H saturation in the subsurface layers. The thickness of the saturated layers could grow under prolonged loading and the H in the layers remain long or hard to remove. Both the growth of the thickness of the saturated layers and the deep penetration of H into the bulk could result in significantly large H retention in W and dissipate the advantage of W as plasma facing wall.