Development of the first mirrors for ITER plasma diagnostics based on rhodium

nanocrystalline coatings

V.V. Kedrov, N.V. Klassen, G.V. Strukov (ISSP RAS), D.V. Orlinskyi (“Kurchatov Institute”),A.F. Bardamid, O.G. Kolesnik, K.I. Iakimov (Kiev University),V.S. Voitsenia, V.G. Konovalov, I.V. Ryjkov, S.I. Solodovchenko, A.F. Shtan’ (Kharkov Institute of Physics and Engineering)

Reflectivity of various metals

Rhodium is one of the best materials for the first mirrors due to:● high melting point ● low rate of sputtering;● good reflectivity

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efl

ec

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n c

oe

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Wavelength , nm

Al

Rh Cu Ag

W

Mo

Disadvantages of bulk Rh mirrors high cost of the bulk material (more than

100,000 USD/ kilogram), resulting in the cost of one bulk mirror more than 30,000 USD;

inevitable deterioration of the optical smoothness of the reflecting surface due to its vapor etching during sputtering (the mean dimensions of the grains are in the range 1 – 10 micrometers, so evaporation of the material from the surface results in etching of intergrain boundaries and corresponding scattering of the light)

First experiments on Rh film mirrors

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Rh on Cu R

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Thickness of sputtered layer, um

650nm

#3 #4

#3 #4

400nm Res. pow.

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mm

Differences in sputtering perfomance of surfaces of various mirrors

Good mirror Bad mirror

The both of these problems are solved by preparation of the rhodium mirrors based on thin

film Rh coatings (with the thickness about 10 μm)

The total volume of rhodium and its cost are decreased by about 100 times;

The optical smoothness of the reflecting surface during sputtering of several micrometers can be stabilized by preparation of nanocrystalline structure of the rhodium coating. In this case the distances between intergrain boundaries are much less than the light wavelength, so scattering of the light by the boundaries can be neglected).

This opportunity has been confirmed by our experiments on sputtering of Rh coatings deposited by electroplating

In these experiments we varied

Material of substrate (copper, brass, copper – nickel alloys, stainless steel, )

Procedure of substrate preparation (abrasive polishing, deformation polishing) Concentration of the electrolythe (from 10% to 40 % of water solution

of sulfur acid) Concentration of rhodium in the electrolythe (by dissolving of rhodium

sulfate) Material and dimensions of the anode (rhodium, platinum, nickel) The distance between the anode and the substrate Procedure of the chemical activation of the substrate Procedure of deposition of intermediate layer (nickel, nickel-silver alloy) Current density Rate of the barbotage of the solution Temperature of the solution Procedure of finishing processing of the coating

Testing of the mirrors with Rh coatings

The samples were subjected to bombardment in deuterium plasma (0.1 – 1000 eV) The optical characteristics were measured as functions of the bombardment duration and thickness of the sputtered layer:

Spectroscopy of optical reflection Integral optical reflection In parallel the morphology of the surface was studied as

the function of the sputtering time by means of scanning electron microscopy

X-Ray diffractometry and adhesion measurements have been made as well

Correlation between the degree of stability the optical parameters, surface morphology and parameters of

nanocrystalline structure has been found

The most stable mirrors have nanocrystalline structure of Rh coating with mean dimensions of the grains between 10 and 30 nm

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Rh film mirrors, λ = 600им

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Reflection coefficient, %

Bombardment duration, minutes

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Correlation between the degree of stability the optical parameters, surface morphology and parameters of

nanocrystalline structure has been found

Good mirror Moderate mirror Bad mirror

Now we are ready to develop the technological chain for mass production of the first mirrors of this kind for ITER:

Preparation of substrates. Cleaning of the substrates in ultrasonic

baths. Activation of the substrates in acid

solutions. Rhodium deposition by electroplating. Finishing processing of the mirrors. Cleaning of the mirrors. Exit control of the mirrors (optical

reflectometry and X-Ray diffractometry)

Scheme of electroplating deposition of Rh film

Rh solutionsubstrate anode

Development of technology of mass production of Rh film mirrors

The total duration of the work: 12 months The final results: the experimental

technological line with optimized technological procedures at each step

Amount of specialists involved: 7 persons Total cost of the work: about 100,000 USD Estimation of production cost of one mirror

(100 mm diameter): 500 USD

Deformation polishing of mirrors resulting in surface passivation

die

surface

Radiation hard scintillators based on nanoscopic oxides

radiation defects are attracted to the surface and annihilated

light guide

nanoscintillator

γn

Conclusions

Laboratory technology of electroplating deposition of nanocrystalline rhodium coatings onto substrates from copper alloys has been developed

The first mirrors manufactured by electroplating deposition of nanocrystalline rhodium films onto substrates from copper alloys demonstrate high reflectivity and its good stability under sputtering of several micrometers.

Technology of mass production of the first mirrors by means of rhodium deposition onto substrates from copper alloys can be developed in one year.

The production cost of the rhodium film mirror with 100 mm diameter stable to ion sputtering is estimated as 500 USD

Application of finishing deformation polishing of rhodium anf other mirrors can decrease significantly the rate of deposition of carbon – hydrate films due to effective passivation of the surface of the mirror.