Broadband dielectric mirrors for optical diagnostics in ITER

Specially designed multilayered dielectric mirrors are able to provide reflectivity over 95% in visible range and hence can help to improve the performance of optical diagnostics for use in ITER. Samples with TiO2/SiO2 and Nb2O5/SiO2 coatings were tested under heat loads following neutron irradiation to verify their resistance to ITER-relevant conditions. All samples survived the neutron irradiation. Reflectivity of TiO2/SiO2 samples degraded after heating, whereas Nb2O5/SiO2 samples showed no significant changes in all the tests. Additionally, influence of hydrocarbon contamination on samples reflectivity was experimentally examined. As a result, such an effect was found not to be significant, and Nb2O5/SiO2 coating is regarded to be acceptable for ITER applications.