Data for Erosion and Tritium Retention in Beryllium Plasma-facing Materials

There is very active interest at present in the properties of beryllium as a wall material exposed to plasma in a fusion reactor environment. The planned plasma-facing materials for nuclear operation in ITER are beryllium and tungsten: beryllium for most of the vacuum vessel and tungsten for the regions of highest heat load. A new "ITER-Like" Be-W vacuum vessel wall has been installed on the Joint European Torus (JET) experiment and plasma experiments on that machine are to start again in August 2011. Beryllium has in its favour good heat conductivity, strong gettering capability, high tolerance as a plasma impurity and low nuclear activation. On the other hand, erosion and tritium retention are issues of concern. The central issues are erosion under regular heat and particle loads from the plasma, melting and ablation under extreme (pulsed) loads, tritium retention, and ways to extract trapped tritium. It must be taken into account that the material and surface properties are highly variable as a result of interaction with impurities (primarily C, N, O, Ne and Ar), implantation of H and He, redeposition of eroded Be and resolidification of melt layers. The CRP on "Data for erosion and tritium retention in beryllium plasma-facing materials" is intended to enhance the knowledge base on fundamental particle-material interaction processes involving beryllium in the fusion plasma environment. The key processes to be studied in the CRP are physical and chemical sputtering by H, He and Be, which release beryllium impurities into the plasma, trapping and reflection of hydrogen (H, D, T) on beryllium surfaces, the transport of hydrogen in beryllium and means to extract trapped tritium. The CRP will emphasize data for the relevant mixed materials, especially Be-(H,D,T,He), Be-C, Be-N, Be-O and ternary and higher mixtures, and data for the principal plasma impurities as projectiles. The most important projectiles are therefore H, D, T, He, Be, C, N, O, Ne and Ar. The CRP will bring together experimentalists and computational theorists that are engaged in studies of plasma-material interaction with beryllium and related mixed materials and of hydrogen migration in solid beryllium. The behaviour of the eroded material in the plasma belongs to our CRP on "Light Element Atom, Molecule and Radical Behaviour in the Divertor and Edge Plasma Regions". Macroscopic surface processes such as melting and ablation under intense (pulsed) heat loads are not emphasized in the proposed CRP. Materials issues such as neutron damage, fabrication and structural properties are outside the scope of the CRP.