MOLIBDENUM MIRRORS WITH COLUMN NANOGRAIN REFLECTING COATING AND EFFECT OF ION- STIMULATED DIFFUSION BLISTERRING RRC «Кurchatov Institute» А.V. Rogov, К.Yu.Vukolov

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

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

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

Modeling device – DC magnetron sputtering system Sputtering in gas mixture: D 2 + small part of air (N 2 + O 2 ), for modeling heavy addition in ITER; Middle energy of sputtering ions (D +, N +, O + ): Conservation of fraction material sputtered by light components (D, T, He charge-exchange atoms in ITER and D +, D 2 + in magnetron): DC-magnetron schematic diagram: 1- magnetic field; 2 – ionization zone; 3 - cathode (sputtering mirror); 4 – erosion zone, 5 – anode. 12 Ions energy distribution in magnetron and charge-exchange atoms in ITER Ions fluence (F) distributions due to mirror diameter with different sputtering times (T) 3 Modeling parameters:

Reflectance R, diffusion scattering D ( =635 nm) and surface morphology dependence from ions fluence and sputtering time Т for SC and NC mirrors. Macroblisters on NC mirrors after sputtering during Т=135 min. 10  m 300 мкм 10  m300  m

Dependence blisters evolution against ions fluence. Sputtering time Т = 10 min. 5 m5 m5 m5 m5 m5 m 234 Reflectance R, diffusion scattering D ( =635 nm) and surface morphology dependence from ion fluence and sputtering time Т for SC mirrors. 1  m 1 Microblisters  - Т = 10 min  - Т = 135 min F  1,2  ions/m 2 F  1,2  ions/m 2 F  2,0  ions/m 2 F, ions/m 2 DR

Main conclusions: Nanocrystal Mo mirrors have high stability to sputtering, similar to single crystal Mo mirrors Large mirrors can be manufactured on polished polycrystalline substrate by 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 mirrors was mainly determined by blistering in fluence range up to ions/ m 2, 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 blistering is needed to understand this effect possibility in ITER