Commercial dielectric coated mirrors for ITER diagnostic applications

We report the results obtained for different types of dielectric coated mirrors obtained from two manufacturers. They include standard visible to IR, UV enhanced, and multilayer enhanced narrow range (“cold”) mirrors. Good radiation resistance has been observed for all the mirrors tested, with no marked degradation following gamma irradiation up to doses of 50 and 60 MGy at 170 °C in dry nitrogen atmosphere, but mirrors provided as identical in the same batch have very different reflectivities (as previously reported for other manufacturers). Furthermore specifications given for the overcoating materials are completely unreliable. The preference for SiO2 overcoating rather than SiO for corrosion protection has been confirmed.