Functional materials for tokamak in-vessel systems-status and developments

The challenge to be faced in ITER and DEMO, as well as future fusion power plants (PPs), by the insulating (functional) materials for use not only in the magnetic coils and heating systems but for safety and control diagnostics is daunting. The available data on thermomechanical properties (strength, swelling, thermal conductivity) indicate that suitable materials are available for doses >1 dpa. However, for the important physical properties which degrade at far lower doses, data are generally only available for doses << 1 dpa, corresponding at most to ITER expectations. To address this, the selection and development of potential radiation hard materials and components for diagnostic, H&CD, and other systems for DEMO and PPs is urgently needed, and will also assist in defining the materials test requirements for materials test reactors and IFMIF. This paper reviews the current data and basic knowledge for materials required for optical, DC electric, and AC/RF dielectric applications. A short discussion of the associated R&D needs/requirements deduced from missing or limited irradiation data is also presented.