Investigations on Investigations on

Applicability of Dielectric Applicability of Dielectric

Mirrors for ITERMirrors for ITERIlya OrlovskiyOrlovskiy, Konstantin Vukolov, Konstantin Vukolov

10th ITPA Meeting Group, Moscow, Russia

MotivationMotivation

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.

3rd mirror 4th mirror

Neutron flux* 2.2·1012 n/cm2s 4.7·1010 n/cm2s

Fluence (1 year**) 1.1·1019 n/cm2 2.4·1017 n/cm2

Temperature*** 150 – 250ºC 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 2003-2004Samples 2003-2004

LabelWorking

range, nm

CoatingManufacturer

MaterialsNumber of layers

PT# 590 – 740 TiO2 / SiO2

13 “Luch”, Podolsk, RussiaPZ# 590 – 670

ZrO2 / SiO2

15

LT# 550 – 650 TiO2 / SiO2

17 “LOGF”, Lytkarino,

RussiaLZ# 640 – 740 ZrO2 / SiO2

23

Substrate(SiO2 – KS-4V)

High refractionmaterial

(TiO2 or ZrO2)

Low refractionmaterial

(SiO2)

25 mm

~0

.00

2 m

m2

mm

The samples were made

of alternating layers of

TiO2/SiO2 and ZrO2/SiO2 on

silica glass substrate.

Reflectance of the samples

reaches 99% at different

wavelengths depending on

material and number of layers.

incident

lightre

flected lig

ht

Heating in vacuum 2003-2004Heating in vacuum 2003-2004

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 IrradiationNeutron Irradiation

Neutron spectrum in the active zone of IR-8 reactor

The coatings of the samples irradiated to 1019 n/cm2 remained

undamaged.

The working range shifted slightly towards short wavelengths.

Reflectance before and after the irradiation

Samples 2005-2006Samples 2005-2006

# Sample Workingrange

Coating Substrate Size

1LF

400-670 nm

TiO2/SiO2

23 layer

s

Fused silica KU-1 100x10

mm2 LG Silica glass K-8

3SF

Fused silica KU-1 25x2 mm

4 SG Silica glass K-8

Heating in vacuum 2006Heating 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%.

ConclusionsConclusions

• 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 plansFurther 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.