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Ion-Driven Permeation of Deuterium through Tungsten Motivation Permeation experiment Results Next steps A. V. Golubeva, M. Mayer, J. Roth
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Ion-driven permeation (IDP) Hydrogen recycling Deep diffusion Hydrogen inventory in the bulk, cooling water channels Motivation
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Motivation (2) In this work: A new PERMEX set-up for investigation of IDP through metal (W) membranes Permeation experiments with W foils Influence of surface impurities on IDP through W foils Lack of data on ion-driven permeation through W No data on ion-driven permeation through coated W
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Experimental Temperatures22-750 0 C ParticlesD 2 + or D 3 + Energies200 eV – 3 keV/D Flux:10 17 – 10 18 D/m 2 s Normal incidence Background<5 10 -9 mbar Ion gun PERMEX set-up Registration of HD (main component for W) D 2 and other masses - by QMS QMS calibration by set of calibrated D 2 leaks Membrane backside cleaning – by 1.5 keV Ar +, 5 10 17 Ar/m 2 s Calibrated D 2 leaks
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AuthorAnderlNakamuraPresent work Т, К610-823550-770< 813-1023 Incident particlesH, DD, TD E, keV/particle110.2 – 3 Flux, part./m 2 s 6.5 10 19 5 10 18 - 10 19 10 17 - 10 18 Backside cleaningNo Yes Membr. thickness25 µm, 50 µm 0.1 mm/SS 25 µm, 50 µm50 µm – 0.3 mm MaterialsPCW, W coatings on SS PCW Measured experimental data Shapes of permeation curves Perm. flux (F perm ) via material of membrane Lag time (Т) F perm (Т) F perm (F 0 ) Isotope effect F perm (Т) Lag time (Т) F perm (surface conditions) ModellingEnergy & Concentr. of traps Trapping energyRecombination coefficients Comparison with other IDP W experiments
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Materials investigated - 99.98% W foils NRA on top of both as received W foils are present O2.5∙10 16 O/cm 2 3.6 nm WO 2 (and comparable C3∙10 16 C/cm 2 thickness of C) 50 µm (Unknown), Not pre-annealed SEM: grains up to 40 µmSEM: grains 1 – 5 µm 50 µm (Plansee), Not pre-annealed 0.3 mm (Goodfellow), pre-annealed (1500 K, 3 hours)
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Permeation curve without front side cleaning Typical permeation curve at first irradiation, T=700 C, material without specification Spike (due to oxide layer on front side) presents at T>700 0 C only at first implantation D (200 eV) => W 50 µm T=700 0 C
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Permeation curves &Typical times 20 min – time to remove impurities from front side by sputtering (Note: D (200 eV) does not create displacement defects in W) F implanted =F 0 *(1-R n ) Reflection coefficient R n – from modeling Permeating flux / implanted flux 50 µm not annealed foil
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Influence of backside cleaning Backside was not cleaned Backside was cleaned An order of magnitude increase after removal of oxide layer at outlet side D on 50 µm W
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Reproducibility of results Backside was not cleaned between implantations Backside was cleaned between implantations Shape (e.g. „Lag time“) – repeatable Maximum decreases from implantation to implantation Reproducible (both “lag time” and amplitude of curve) D on W, 50 µm, 600 0 C, 10 18 D/m 2 Backside was cleaned after sample installation From sample to sample – 20 % difference in permeation rate
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Oxide influence: Backside cleaning Plansee 50 m W, 200 eV/D, 2 10 17 D/m 2 s Backside cleaning 5 times increase of permeation flux b3 Surface conditions do not change during at least 2 days Permeation depends strongly on surface conditions 2E-3 4E-4 Repeatability from sample to sample – 30 %
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Nakamura: permeating flux is proportional to incident flux, F=kF 0 in the range 2.5∙10 18 – 10 19 D/m 2 s PERMEX: F=kF 0 in the range 5∙10 16 -2∙10 17 D/m 2 s To compare results, we consider permeation rate F/F 0 Previously defined Permeation rates through W can be underestimated Oxide influence: Backside cleaning 2003
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Database Permeation strongly depends on material structure (2 times difference for 99.98% W foils of the same thickness but different grain sizes) Possibility of experiments with thick (0.3 mm) membranes is demonstrated Grains ~ membrane thickness
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Effective diffusion coefficients Large influence of traps L – foil thickness, - lag time
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Conclusions PERMEX set-up developed and build allows IDP experiments with control of both membrane sides First D on W permeation data obtained for 550-750 0 C 200 eV/D permeation ratio (F perm /F 0 ) = 5×10 -4 (Plansee 50 µm, as received) Permeation spike observed at 700 0 C sputtering of oxide layer on the inlet surface Surface layer conditions strongly influence permeation rate: backside cleaning increases permeation by factor 5 Material structure influences significantly IDP
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Future plans Permeation through W with different coatings on front side (oxide, carbide) PhD thesis in collaboration with MEPhI (A. Pisarev) Modeling of IDP to obtain recombination coefficients
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