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Modelling of ion - driven deuterium retention in W O.V. Ogorodnikova in collaboration with

Modelling of ion - driven deuterium retention in W O.V. Ogorodnikova in collaboration with J. Roth and M. Mayer MPI für Plasmaphysik, EURATOM Association, Garching, Germany. Ion implantation and TDS. D retention in W has been studied in ion beam experiments: monoenergetic ion beam

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Modelling of ion - driven deuterium retention in W O.V. Ogorodnikova in collaboration with

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  1. Modelling of ion - driven deuterium retention in W O.V. Ogorodnikova in collaboration with J. Roth and M. Mayer MPI für Plasmaphysik, EURATOM Association, Garching, Germany

  2. Ion implantation and TDS D retention in W has been studied in ion beam experiments: monoenergetic ion beam E = 200 eV D+ to 3 keV D+ T = 300 K to 600 K D inventory in W increases as a square root of fluence at RT => diffusion-limited trapping. Ogorodnikova O.V., Roth J., Mayer M., J. Nucl. Mater. 313-316 (2003) 469-477

  3. Ion implantation and TDS D retention in W has been studied in ion beam experiments: monoenergetic ion beam E = 200 eV D+ to 3 keV D+ T = 300 K to 600 K D inventory in W increases as a square root of fluence at RT => diffusion-limited trapping. Most of D are trapped in the bulk at high fluences. Ogorodnikova O.V., Roth J., Mayer M., J. Nucl. Mater. 313-316 (2003) 469-477

  4. Ion implantation and TDS TDS shows two peaks. Both peaks grow with fluence. Second peak (high-temperature) grows faster.

  5. Ion implantation and TDS Pre-implantation with intermediate TDS increases the second peak.

  6. Modelling of D retention in PCW Desorption, J0 trapping Implantation, I0 Permeation, JL

  7. Modelling of D retention in PCW Ion-induced traps Natural traps Desorption, J0 trapping Implantation, I0 Permeation, JL

  8. Dislocations, Grain boundaries Bubbles, Vacancies Modelling of D retention in PCW Diffusion model with two kinds of traps describes well experimental data.

  9. Modelling of D retention in PCW 0.85 eV 1.45 eV Ion-induced traps distributes near the surface and natural traps distributes along whole W thickness W(x,t)=Wm(1 – exp(-(1-r)I0y(x)ht/Wm)) Rate of defect production h = f (initial traps, ion flux, ion energy, temperature)

  10. Dislocations, Grain boundaries Bubbles, Vacancies Modelling of D retention in PCW Ion-induced traps distributes near the surface and natural traps distributes along whole W thickness W(x,t)=Wm(1 – exp(-(1-r)I0y(x)ht/Wm)) Rate of defect production h = f (initial traps, ion flux, ion energy, temperature)

  11. Modelling of D retention in PCW Rate of defect production is higher for pre-implantation with intermediate TDS Ion-induced traps distributes near the surface and natural traps distributes along whole W thickness W(x,t)=Wm(1 – exp(-(1-r)I0y(x)ht/Wm)) Rate of defect production h = f (initial traps, ion flux, ion energy, temperature)

  12. Modelling of D retention in PCW Ion-induced traps distributes near the surface and natural traps distributes along whole W thickness

  13. Modelling of D retention in PCW • Which kinds of ion-induced defects of 1.45 eV can be produced by low energy ions? => • - 200 eV cannot produce vacancies (Eth=860 eV) • - D self-aggregation in clusters due to stress field created by implanted deuterium

  14. Modelling of D retention in PCW • Why D agglomerates in clusters only near the implantation surface? => • Because of stress field induced by ion implantation

  15. D agglomeration in clusters and bubble growth => => Tension and stress=> Displacement of W atom=> Di-vacancy=> Bubble growth D traps by vacancy Several D trap by vacancy Tension and stress=> Dislocation (loop punching?) • Conditions for bubble formation: • Saturation in D concentration • Saturation in vacancies

  16. Temperature effect An increase of the temperature results in a decrease of D retention for recrystallized ´virgin´ PCW At 400 K D retention increases with fluence faster than at RT

  17. Temperature effect D retention decreases with temperature for ´virgin´ W An increase of the temperature results in a decrease of D retention for recrystallized ´virgin´ PCW Model describes well temperature dependence.

  18. Temperature effect D retention decreases with temperature for ´virgin´ W. Most of D are in the bulk. An increase of the temperature results in a decrease of D retention for recrystallized ´virgin´ PCW Model describes well temperature dependence.

  19. Implantation energy effect Lower D retention for 3 keV than for 200 eV at high fluences

  20. Implantation energy effect Increase of the stress field => increase of the diffusion coefficient

  21. Implantation energy effect Increase of the stress field => increase of the diffusion coefficient

  22. Implantation energy effect Calculated depth profiles Increase of the stress field => increase of the diffusion coefficient

  23. Conclusions • D retains in W in ion-induced defects and natural defects • An increase of ion energy (or/and ion flux) results in an increase of the stress field in the implantation region. As a result the diffusion coefficient near the implantation region increases. • Both no recrystallization and intermediate TDS (annealing up to 1200 K) increase the rate of defect production Ion-induced defects are produced during implantation by deuterium self-aggregation due to the stress field induced by the incident ion flux The rate of ion-induced defect production depends on the energy of the incident ions, ion flux, sample temperature and initial trap concentration

  24. Discussion

  25. Implantation energy effect Increase of the stress field => increase of the diffusion coefficient

  26. Implantation history effect D retention decreases with temperature for ´virgin´ W. D retention has a maximum for re-used W. An increase of the temperature results in a decrease of D retention for recrystallized ´virgin´ PCW Model describes well temperature dependence.

  27. Implantation history effect Recrystallized W As-received W after multiple implantation D retention in the second peak decreases with temperature for recrystallized W D retention in the second peak increases with temperature for re-used W

  28. Implantation history effect Intermediate TDS increases the amount of initial high-temperature traps Calculations using the higher rate of defect production are in a good agreement with experiments. An increase of the temperature results in a decrease of D retention for recrystallized ´virgin´ PCW Model describes well temperature dependence.

  29. Modelling of D retention in PCW • The increase of amount of initial traps increases the rate of deuterium cluster formation • Both intermediate TDS and no recrystallization increase the amount of initial traps

  30. Deuterium retention in W W: 3 keV D+, RT

  31. Conditions for cluster formation and bubble growth • Conditions for cluster formation in W • Initial amount of defects • Low solubility and diffusivity • Low porosity • Acceleration of rate of cluster growth • High ion flux or/and ion energy

  32. Implantation energy effect Increase of the stress field => increase of the diffusion coefficient

  33. R & D Experiments • off-normal events & ELM´s • D retention in damage W n-irradiation • He-irradiation • D retention at high implantation temperature (T=800 K - 1000 K) at different ion fluxes Modelling • Competition of erosion/diffusion • Soret effect • Maxwellian energy distribution • Diffusion in tension field

  34. Is D retention in W a problem for ITER ? • W as a divertor • Tplasma: 1-20 eV • Particle flux : 1022 – 1024 /m2/s • Tw : ~1000 K • Competition of erosion/diffusion • Deposition of impurities, codeposition ? • Damages in the near surface region by off-normal events • Diffusion in tension field

  35. Is D retention in W a problem for ITER ? • W as a FW • Tplasma: 1-5 eV ? • Particle flux : ~1020 /m2/s • Tw : ~500 K ? • W as a divertor • Tplasma: 1-20 eV • Particle flux : 1022 – 1024 /m2/s • Tw : ~1000 K • Temperature of W can be important • Diffusion in tension field • Competition of erosion/diffusion • Deposition of impurities, codeposition ? • Damaged by off-normal events near surface region • Diffusion in tension field

  36. Is D retention in W a problem for ITER ? • W as a FW • Tplasma: 1-5 eV ? • Particle flux : ~1020 /m2/s • Tw : ~500 K ? • W as a divertor • Tplasma: 1-20 eV • Particle flux : 1022 – 1024 /m2/s • Tw : ~1000 K • Temperature of W can be important • Diffusion in tension field • Competition of erosion/diffusion • Deposition of impurities, codeposition ? • Damaged by off-normal events near surface region • Diffusion in tension field • Bulk retention can be of concern

  37. Is D retention in W a problem for ITER ? • W as a FW • Tplasma: 1-5 eV ? • Particle flux : ~1020 /m2/s • Tw : ~500 K ? • W as a divertor • Tplasma: 1-20 eV • Particle flux : 1022 – 1024 /m2/s • Tw : ~1000 K • Temperature of W can be important • Diffusion in tension field • Competition of erosion/diffusion • Deposition of impurities, codeposition ? • Damaged by off-normal events near surface region • Diffusion in tension field • Bulk retention can be of concern • n-irradiation – strong trapping in vacancies distributed over all W thickness

  38. Talk outline • Experimental data • Modelling of D retention in PCW • Temperature effect • Implantation history effect • Ion energy effect

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