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

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

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

Experimental Temperatures C ParticlesD 2 + or D 3 + Energies200 eV – 3 keV/D Flux:10 17 – D/m 2 s Normal incidence Background<5  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  Ar/m 2 s Calibrated D 2 leaks

AuthorAnderlNakamuraPresent work Т, К < Incident particlesH, DD, TD E, keV/particle110.2 – 3 Flux, part./m 2 s 6.5   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

Materials investigated % W foils NRA  on top of both as received W foils are present O2.5∙10 16 O/cm 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)

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

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

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

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, C, D/m 2 Backside was cleaned after sample installation From sample to sample – 20 % difference in permeation rate

Oxide influence: Backside cleaning Plansee 50  m W, 200 eV/D, 2  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 %

Nakamura: permeating flux is proportional to incident flux, F=kF 0 in the range 2.5∙10 18 – D/m 2 s PERMEX: F=kF 0 in the range 5∙ ∙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

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

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

Conclusions PERMEX set-up developed and build  allows IDP experiments with control of both membrane sides First D on W permeation data obtained for C 200 eV/D  permeation ratio (F perm /F 0 ) = 5×10 -4 (Plansee 50 µm, as received) Permeation spike observed at 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

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