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RRC «К urchatov Institute »

This research explores the design and characteristics of column nanocrystal (NC) molybdenum mirrors with a reflective coating, focusing on their resistance to ion-stimulated sputtering, which is critical for ITER applications. Single crystal mirrors show significant sputtering resistance, but advancements in NC mirrors present a viable alternative for larger sizes while maintaining optical quality. This study details experimental samples, fabrication methods, and parameters affecting performance under ITER conditions, highlighting the importance of structure and stability in maximizing mirror lifespan and functionality.

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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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