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Ion-Driven Permeation of Deuterium through Tungsten

Ion-Driven Permeation of Deuterium through Tungsten. A. V. Golubeva, M. Mayer, J. Roth. Motivation Permeation experiment Results Next steps. Motivation. Ion-driven permeation (IDP) Hydrogen recycling

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Ion-Driven Permeation of Deuterium through Tungsten

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  1. Ion-Driven Permeation of Deuterium through Tungsten A. V. Golubeva, M. Mayer, J. Roth • Motivation • Permeation experiment • Results • Next steps

  2. Motivation • Ion-driven permeation (IDP) • Hydrogen recycling • Deep diffusion  Hydrogen inventory in the bulk, cooling water channels

  3. Motivation (2) • Lack of data on ion-driven permeation through W • No data on ion-driven permeation through coated W • 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

  4. Ion gun PERMEX set-up Calibrated D2 leaks Experimental Temperatures 22-750 0C Particles D2+ or D3+ Energies 200 eV – 3 keV/D Flux: 1017 – 1018 D/m2s Normal incidence Background<510-9 mbar Registration of HD (main component for W) D2 and other masses - by QMS QMS calibration by set of calibrated D2 leaks Membrane backside cleaning – by 1.5 keV Ar+, 51017 Ar/m2s

  5. Comparison with other IDP W experiments

  6. Materials investigated - 99.98% W foils 50 µm (Plansee), Not pre-annealed 0.3 mm (Goodfellow), pre-annealed (1500 K, 3 hours) 50 µm (Unknown), Not pre-annealed SEM: grains 1 – 5 µm SEM: grains up to 40 µm SEM: grains 1 – 5 µm NRA  on top of both as received W foils are present O 2.5∙1016 O/cm2 3.6 nm WO2 (and comparable C 3∙1016 C/cm2 thickness of C)

  7. Permeation curve without front side cleaning Typical permeation curve at first irradiation, T=700 C, material without specification D (200 eV) => W 50 µm T=7000C Spike (due to oxide layer on front side) presents at T>7000C only at first implantation

  8. Permeation curves &Typical times Permeating flux / implanted flux 50 µm not annealed foil Fimplanted =F0*(1-Rn) Reflection coefficient Rn – from modeling 20 min – time to remove impurities from front side by sputtering (Note: D (200 eV) does not create displacement defects in W)

  9. Influence of backside cleaning D on 50 µm W Backside was cleaned Backside wasnot cleaned An order of magnitude increase after removal of oxide layer at outlet side

  10. Reproducibility of results D on W, 50 µm, 600 0C, 1018 D/m2 Backside was cleaned after sample installation Backside wasnot cleaned between implantations Backside was cleaned between implantations Reproducible (both “lag time” and amplitude of curve) • Shape (e.g. „Lag time“) – repeatable • Maximum decreases from implantation • to implantation From sample to sample – 20 % difference in permeation rate

  11. Oxide influence: Backside cleaning Backside cleaning  5 times increase of permeation flux Plansee 50 m W, 200 eV/D, 21017 D/m2s 2E-3 Permeation depends strongly on surface conditions b3  Surface conditions do not change during at least 2 days 4E-4 Repeatability from sample to sample – 30 %

  12. Oxide influence: Backside cleaning Nakamura: permeating flux is proportional to incident flux, F=kF0 in the range 2.5∙1018 – 1019 D/m2s PERMEX: F=kF0 in the range 5∙1016-2∙1017 D/m2s  To compare results, we consider permeation rate F/F0 2003 Previously defined Permeation rates through W can be underestimated

  13. Database Grains ~ membrane thickness 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

  14. Effective diffusion coefficients L – foil thickness,  - lag time • Large influence of traps

  15. Conclusions • PERMEX set-up developed and build allows IDP experiments with control of both membrane sides • First D on W permeation data obtained for 550-7500C • 200 eV/D permeation ratio (Fperm/F0) = 5×10-4(Plansee 50 µm, as received) • Permeation spike observed at 7000Csputtering ofoxide layer on the inlet surface • Surface layer conditions strongly influence permeation rate:backsidecleaning increases permeation by factor 5 • Material structure influences significantly IDP

  16. 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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