Investigations on Applicability of Dielectric Mirrors for ITER Orlovskiy, Konstantin Vukolov Ilya Orlovskiy, Konstantin Vukolov 10 th 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. 3 rd mirror4 th mirror Neutron flux*2.2·10 12 n/cm 2 s4.7·10 10 n/cm 2 s Fluence (1 year**)1.1·10 19 n/cm 2 2.4·10 17 n/cm 2 Temperature***150 – 250ºC 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

Samples Label Working range, nm Coating Manufacturer Materials Number of layers PT#590 – 740TiO 2 / SiO 2 13 “Luch”, Podolsk, Russia PZ#590 – 670ZrO 2 / SiO 2 15 LT#550 – 650TiO 2 / SiO 2 17 “LOGF”, Lytkarino, Russia LZ#640 – 740ZrO 2 / SiO 2 23

Substrate (SiO 2 – KS-4V) High refraction material (TiO 2 or ZrO 2 ) Low refraction material (SiO 2 )  25 mm ~0.002 mm 2 mm The samples were made of alternating layers of TiO 2 /SiO 2 and ZrO 2 /SiO 2 on silica glass substrate. Reflectance of the samples reaches 99% at different wavelengths depending on material and number of layers. incident light reflected light

Heating in vacuum The coatings of the “LOGF” samples were damaged. Working range of “Luch” samples was shifted towards short wavelengths. The coatings remained undamaged. Heating regime Reflectance before and after the heating “LOGF” samples after the heating

Neutron Irradiation Neutron spectrum in the active zone of IR-8 reactor The coatings of the samples irradiated to n/cm 2 remained undamaged. The working range shifted slightly towards short wavelengths. Reflectance before and after the irradiation

Samples #SampleWorking range CoatingSubstrateSize 1 LF nm TiO 2 /SiO 2 23 layers Fused silica KU-1  100x10 mm 2 LGSilica glass K-8 3 SFFused silica KU-1  25x2 mm 4 SGSilica glass K-8

Heating in vacuum 2006 The samples were heated in vacuum oven in two regimes under 10 3 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.