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RRC «К urchatov Institute »

MOLIBDENUM MIRRORS WITH COLUMN NANOGRAIN REFLECTING COATING AND EFFECT OF ION - STIMULATED DIFFUSION BLISTERRING. А. V . Rogov , К. Yu . Vukolov. RRC «К urchatov Institute ». Influence of mirrors structure to physical sputtering resistant. 1.

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RRC «К urchatov Institute »

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  1. MOLIBDENUMMIRRORSWITHCOLUMNNANOGRAIN REFLECTINGCOATINGANDEFFECTOF ION-STIMULATEDDIFFUSIONBLISTERRING А.V. Rogov, К.Yu.Vukolov RRC «КurchatovInstitute»

  2. Influence of mirrors structure to physical sputtering resistant 1 Single crystal (SC)polishedmirrors have the better resistant to sputtering . Technological limit for SC mirrors size. For Mo SC mirror:  140 mm [V.S. Voitsenia et. al.3-th Conference Fusion and Plasma Phis., 2003.]. As perspective large size mirrors for ITER we suggest : mirrorswith reflected layer, formed by densely packed columnnanocrystallites, oriented perpendicular to substrate surface, named: nanocrystal (NC) mirrors   2 a  b Structure requirements: •     constant ofRduring sputtering; •     optical quality equal to substrate; •  max spattering depth  time stability. • Structure of NC mirror: • – reflectinglayer; • (b) – polishedsubstrate. Purpose ofwork:Design of experimentalsamplesofMo NC-mirrors, investigateits optical properties and stability to sputtering in ITER conditions.

  3. Design and structure of experimental samples MoNC-mirrors . 1 2 1 m Column nano-structure [Thornton J.A. // J. Vac. Sci. Technol, 1974, Vol. 11, № 4]. 3 Parameters of Mo NC - mirrors: Substrate: single crystalМо; Evaporatedmaterial:Мо; Method:DC- magnetron evaporation; Mirror size:21 mm×1.5 mm; Thicknessreflecting layer:1.5 m; Crystallites size:  50×100×1500 nm; Crystallites size across

  4. Selection ofmodeling conditions for sputtering inITER 1 • Critical diagnostic system:MSE andCXRS • (= 470656 nm; Size:  500x300, 350x90 mm) Applied calculation model take account of: First wall • Charge-exchange atoms:D, T, He, Be, C • Energetic distribution of charge-exchange atomson the first wall in ITER: • Model for calculate components composition: • nBe=nC • nHe=0.1(nD+nT) • Z = 1,69 2 (E), at m-2 c-1 E, eV [Mayer M. e.al. - Plenum Press, New York, 1998] Basic data for experimental simulation sputtering of first mirror inITER: • Fluensduring 1 year(N=1000, Т=500 s):Ф = 1025 atoms m-2; • Middleenergycharge-exchange atoms: E = 250 eV; • Erosion on account heavy elements (Be, C): 20%; • Optical probe irradiation :  = 632,8nm (He-Ne- laser)

  5. Modeling device – DC magnetron sputtering system 1 2 DC-magnetron schematic diagram: 1- magneticfield;2– ionization zone; 3- cathode (sputtering mirror);4– erosion zone, 5 – anode. Ions energy distributionin magnetron andcharge-exchange atoms in ITER Modeling parameters: 3 • Sputtering in gas mixture: D2 + small part of air (N2 + O2), for modeling heavy addition in ITER; • Middle energy of sputtering ions (D+ , N+, O+): • Conservation of fractionmaterialsputtered bylightcomponents (D, T, He charge-exchange atomsin ITER and D+, D2+ in magnetron): Ions fluence (F) distributionsdue to mirror diameterwith different sputtering times (T)

  6. Reflectance R, diffusion scattering D ( =635 nm) andsurfacemorphologydependencefrom ions fluence and sputtering time Т forSCandNCmirrors. 300 m 10 m 10 m 300 мкм Macroblisterson NC mirrors after sputtering duringТ=135 min.

  7. Reflectance R, diffusion scattering D ( =635 nm) andsurfacemorphologydependencefrom ion fluence and sputtering time Т forSCmirrors. 1 D R 1 m Microblisters  - Т = 10 min  - Т = 135 min F,ions/m2 F,ions/m2 2 3 4 5m 5m 5m F1,21023 ions/m2 F1,21024 ions/m2 F2,01024 ions/m2 Dependence blisters evolutionagainst ions fluence.Sputtering time Т=10 min.

  8. Main conclusions: • Nanocrystal Mo mirrorshave highstabilityto sputtering, similar to single crystalMo mirrors • Large mirrors can be manufactured on polished polycrystalline substrateby means of proposal technology • The effect of ion-stimulated diffusion blistering was discovered.The presence of surface film, with properties distinct from substrate properties, required for this effect • Optical quality for nanocrystal and single crystal Mo mirrorswas mainly determined byblisteringin fluence range up to 1025 ions/ m2, that corresponds to sputtering during 1 year on the first wall in ITER • The ion-stimulated diffusion blistering can be reason for dust formation in ITER • The additional study of diffusion blisteringis needed to understand this effect possibility in ITER

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