Perspectives of Use of Diagnostic Mirrors with Transparent Protection Layer in Burning Plasma Experiments

We evaluate using of metal mirrors over-coated with transparent protection layer for the in-vessel diagnostic systems in reactor-grade fusion devices. Ideally, these should satisfy the contradictory demands of high reflectivity and small rate degradation when being bombarded by CX atoms. The serious threat to the performance of diagnostic mirrors is surface contamination with carbon-based material eroded from carbon tiles. Via coupling the protective layer to a bulk mirror we can mitigate the deposit infiuence on the reflectance spectra. The regards are given to survivability in plasma environment of protected coated metallic mirrors.