The use of tungsten in fusion reactors: A review of the hydrogen retentionand migration properties

In the past the role of tungsten as a fusion reactor plasma-facing material has been fairly limited. It has appeared sparingly in tokamaks, but usuall y only for experimental purposes. This is likely to change in the future. T ungsten has a very high threshold for sputtering as well as a high melting point and high thermal conductivity. Applications of tungsten in areas wher e the energy of the plasma particles can be kept below the sputtering thres hold removes the plasma impurity problem often associated with the use of t ungsten in fusion reactors. In the area of recycling and retention, tungste n is unlike carbon and beryllium in that hydrogen appears to stay in soluti on in the metal (at least at low concentrations) and diffuse somewhat class ically. This paper presents a review of the hydrogen isotope retention and migration properties of tungsten as they relate to fusion applications. The review is begun with an examination of past experiments on the diffusivity solubility, and permeability of hydrogen in tungsten. Fusion specific topi cs such as implantation and surface effects are then covered. Trapping is s hown to be an important aspect of understanding hydrogen transport in this material. Blister and bubble formation are also addressed.