Image quality method as a possible way of in situ monitoring of in-vessel mirrors in a fusion reactor

The plasma-facing (first) mirrors in ITER will be subject to sputtering and/or contamination with
rates that will depend on the precise mirror locations. The resulting influence of both these factors
can reduce the mirror reflectance (R) and worsen the transmitted image quality (IQ). This implies that
monitoring the mirror quality in situ is an actual desire, and the present work is an attempt towards
a solution. The method we propose is able to elucidate the reason for degradation of the mirror
reflectance: sputtering by charge exchange atoms or deposition of contaminated layers. In case of
deposition of contaminants, the mirror can be cleaned in situ, but a rough mirror (due to sputtering)
cannot be used anymore and has to be replaced. To demonstrate the feasibility of the IQ method,
it was applied to mirror specimens coated with carbon film in laboratory conditions and to mirrors
coated with contaminants during exposure in fusion devices (TRIAM-1M and Tore Supra), as well as
to mirrors of different materials exposed to sputtering by plasma ions in the DSM-2 plasma stand (in
IPP NSC KIPT).