Functional materials for ITER diagnostic systems – Radiation aspects

ITER will be the first fusion device able to maintain fusion for long periods of time and therefore suitable to test integrated technologies, materials, and physics regimes necessary for the commercial production of fusion-based electricity. Therefore, ITER provides a harsh radiation environment that represents an important challenge for diagnostic systems located in various regions inside the tokamak, in particular the first wall, divertor areas, and ports, but as well ex-vessel areas, where radiation levels are also significantly high for some electronic components. The radiation induced effects in functional materials have been identified and studied in the past in the fusion and fission community. These effects comprise nuclear heating, changes in physical and mechanical properties due to transmutation and displacement damage, radiation induced conductivity (RIC) or radiation induced electrical degradation (RIED) effects on insulators, radiation induced absorption (RIA) for optical materials, radio luminescence observed in fibers and windows, etc. This paper summarizes the current status of the functional material selection for ITER diagnostic systems and the expected radiation conditions in the areas where they are located. Additional testing will be required for some materials and assemblies, such as bolometers and magnetic coils. Special attention is paid to the tests required for qualification of safety important components, such as diagnostic window assemblies and vacuum feedthroughs. Finally, as one of the best ways to reduce the impact of radiation in materials is to develop a proper shielding strategy, some of the shielding options envisaged for ITER are presented and discussed in this paper.