Investigations on Applicability of Dielectric Mirrors for ITER Ilya Orlovskiy, Konstantin Vukolov 10th ITPA Meeting Group, Moscow, Russia
Motivation Multilayered dielectric mirrors could significantly improve light transmission from plasma to detectors if used as the secondary mirrors for optical diagnostics (CXRS, MSE, H-Alpha etc). However, diagnostic elements in ITER will be exposed to significant neutron fluencies and thermal load. Calculated conditions for H-Alpha secondary mirrors in ITER * Neutrons with energy more than 0.1 MeV ** 1000 shots of 500 seconds each, D-T operation *** Will be provided by the cooling system in ITER
reflected light incident light High refraction material (TiO2 or ZrO2) The samples were made of alternating layers of TiO2/SiO2 and ZrO2/SiO2 on silica glass substrate. ~0.002 mm Low refraction material (SiO2) 2 mm Substrate (SiO2 – KS-4V) 25 mm Reflectance of the samples reaches 99% at different wavelengths depending on material and number of layers.
Heating in vacuum 2003-2004 Heating regime “LOGF” samples after the heating Reflectance before and after the heating The coatings of the “LOGF” samples were damaged. Working range of “Luch” samples was shifted towards short wavelengths. The coatings remained undamaged.
Neutron Irradiation Neutron spectrum in the active zone of IR-8 reactor Reflectance before and after the irradiation The coatings of the samples irradiated to 1019 n/cm2 remained undamaged. The working range shifted slightly towards short wavelengths.
Heating in vacuum 2006 The samples were heated in vacuum oven in two regimes under 103 Pa. The heating in regime #1 was followed by the heating in regime #2. The coatings of all the samples remained undamaged. The spectra of both large and small samples show the same behavior. The working range shifted towards long wavelengths. The reflectance in the flat range reduced from 98% down to 96%. The reflectance in the negative peaks reduced down to 80%.
Conclusions • Thermal loads assumingly play the main role in damaging of mirror coating, at least under tested fluences. • Multilayered dielectric mirrors can sustain neutron fluences and temperatures expected for secondary mirrors in ITER. Presently, manufactures are able to provide sufficient adhesion of coating to substrate for the mirrors of a large size. • Working range of dielectric mirrors can be shifted slightly being exposed to the temperatures up to 250°C. Shift direction depends on the coating. • Heating can reduce the reflectance of dielectric mirrors, especially in negative peaks of the spectrum.
Further plans • Continuation of heating tests to find the limits of reflectance degradation. • Design and production of prototypes of dielectric mirrors for H-alpha and CXRS diagnostics. • Testing the prototypes in vacuum oven and nuclear reactor. • Developing specifications for production of diagnostic mirrors for ITER.