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S.M. Deambrosis *^, G. Keppel*, N. Pretto^,

Nb 3 Sn by Liquid Tin Diffusion. S.M. Deambrosis *^, G. Keppel*, N. Pretto^, V. Rampazzo*, R.G. Sharma°, D. Tonini * and V. Palmieri*^. * INFN - Legnaro National Labs ^ Padua University, Science faculty, Material Science Dept ° Interuniversity Accelerator Center, New Delhi.

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S.M. Deambrosis *^, G. Keppel*, N. Pretto^,

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  1. Nb3Sn by Liquid TinDiffusion S.M. Deambrosis*^, G. Keppel*, N. Pretto^, V. Rampazzo*, R.G. Sharma°, D. Tonini *and V. Palmieri*^ * INFN - Legnaro National Labs ^ Padua University, Science faculty, Material Science Dept ° Interuniversity Accelerator Center, New Delhi Padova University, Material Science Dept

  2. 1) Theory Vapor Sndiffusion 2) Literature review 3) Technique choice reasons Liquid Sn diffusion Nb3Sn by liquid Sn diffusion Used system 4) Method “1 Step” process 5) Work in progress “2 Steps” process “Hybrid” process 6) Conclusions

  3. RBCS If T < Tc / 2 Empirically, Rres is found to be dependent on rn too. A metallic behaviour in the normal state is mandatory For low rf losses, a high TC value is not sufficient Theory

  4. Nomogram At T = 4.2 K, f = 500 MHz, s = 4, RBCS depends on Δ and ρn RBCS Ideal R BCS ~ 1 nΩ ~ 10 μΩcm Theory

  5. Literature review Many papers of different authors with different aims: • Nb3Sn by CVD and PVD techniques to compare bulk and film properties • Nb3Sn by bronze process for high field Superconducting Magnets • Nb3Sn RF application: Wuppertal Literature

  6. Wuppertal: Nb3Sn cavity (1.5 GHz) obtained trough Sn vapour phase diffusion (’90s) Literature

  7. Vapor Sn Diffusion Heating system Accelerating structure Sn source Sn source heater Pumping system Laboratory Procedure • Cavity manufactoring • Formation of nucleation centers of Nb3Sn (Nb Surface Anodization + SnCl2 Treatment) • Nb3Sn film growth in a Sn atmosphere (T = 1050-1250°C, t = dozens of h, p(Sn) ~ 10-3mbar) • Cool down and unwanted phases Chemical removal (anodizaton + HF 48%) Technique Choice Reasons

  8. Liquid solute diffusion technique Technique Choice Reasons

  9. Liquid Sn Diffusion? Bulk Nb substrate dipping in a liquid Tin bath Sample Annealing • No nucleation sites on Nb are required • Fast growth of Nb3Sn layer • Deasirable uniform thickness Technique Choice Reasons

  10. Used System Method: used system

  11. Nb3Sn: Phase Diagram Nb3Sn 930°C <Tc phases Method: used system

  12. To Summarise ●Liquid solute diffusion technique choice ●Working T > 930 °C

  13. “1 Step” Process Laboratory Procedure • Bulk Nb Substrate chemical cleaning (10 min in a 1:1:2 solution) • Substarte fixing to feedtrough, vacuum and T reaching (1 day) • Substrate thermalization (30 min - 1 h) • Dipping (few min - 2 h) • Annealing above the Sn bath without opening the chamber(some h) • Residual Sn Chemical removal trials Method: “1 step” process

  14. Nb3Sn photo Residual Sn Sn drop Method: “1 step” process

  15. SEM Image Process T = 1000°C Dipping t = 120’ Annealing t = 14h Post annealing: 5h at 500°C Nb3Sn Nb Method: “1 step” process

  16. XRD spectrum Process T = 1000°C, Dipping t = 30’, Annealing t = 10h Method: “1 step” process

  17. EMPA Analysis Method: “1 step” process

  18. A Superconductive Transition Curve Nb3Sn n°16: 1000°C; 120’+14h+post annealing 500°Cx5h Method: “1 step” process

  19. 6 GHz Cavities • Spinning Technique 2. Surface Treatments • Mechanical polishing • Chemical polishing • Nb3Sn film obtainment 3. Q Factor Measurement Method: “1 step” process

  20. Nb3Sn film obtainment Film production: T = 1025°C tdipping = 15 min, tannealing = 15 h Chemical treatment: HCl 37%, t = 10 min, T = 85°C Method: “1 step” process

  21. Q Factor Measurement Nb3Sn Method: “1 step” process

  22. A Nb3Sn 6 GHz Cavity Method: “1 step” process

  23. To Summarise Nb3Sn with good superconductive properties + Tc = 16,9 K DTc= 0,2 K - Residual Sn traces on the sample surface - Sn rich Phases Presence Method: “1 step” process

  24. “2 Steps” Process Laboratory Procedure • Bulk Nb Substrate chemical cleaning (10 min in a 1:1:2 solution) • Substarte fixing to the feedtrough, vacuum and T reaching (1 day) • Substrate thermalization (30 min - 1 h) • Dipping (few min - 2 h) • System opening to remove Sn bath, vacuum and T reaching (1 day) • Sample annealing without Sn vapor (some h) • Growth film chemical treatment Method: “2 steps” process

  25. Nb3Sn photo Method: “2 steps” process

  26. SEM Images Proc T = 1025°C, Dipp t = 15’, Ann t = 15h Proc T = 1025°C, Dipp t = 5’, Ann t = 20h Method: “2 steps” process

  27. XRD spectra Proc T = 1025°C, Dipp t = 5’, Ann t = 20h Proc T = 1025°C, Dipp t = 5’, Ann t = 10h Method: “2 steps” process

  28. A Superconductive Transition Curve Proc T = 1025°C, Dipp t = 5’, Ann t = 20h Tc (Nb3Sn) = 14,9 K DTc (Nb3Sn) = 0,43 K Method: “2 steps” process

  29. Growth film chemical treatment (HCl) Method: “2 steps” process

  30. Tc and DTc vs THCl Method: “2 steps” process

  31. To Summarise + No Residual Sn traces on the sample surface Worst Nb3Sn film superconductive properties - Tc = 15,2 K, DTc = 0,5 K - Sn rich Phases Presence HCl chemical treatment deteriorates the growth film - Method: “2 steps” process

  32. “Hybrid” Process Laboratory Procedure • Bulk Nb Substrate chemical cleaning (10 min in a 1:1:2 solution) • Substarte fixing to the feedtrough, vacuum and T reaching (1 day) • Substrate thermalization (30 min - 1 h) • Dipping (few min - 2 h) • Sample annealing with Sn vapor (some h) • System opening to remove Sn bath, vacuum and T reaching (1 day) • Sample annealing without Sn vapor (some h) Method: “Hybrid” process

  33. Nb3Sn photo Method: “Hybrid” process

  34. XRD spectrum Proc T = 975°C, Dipp t = 30’, Ann (Sn) t = 2h, Ann t = 5h Method: “Hybrid” process

  35. A Superconductive Transition Curve Proc T = 975°C, Dipp t = 30’, Ann (Sn) t = 2h, Ann t = 5h Tc (Nb3Sn) = 16,6 K DTc (Nb3Sn) = 0,28 K Method: “Hybrid” process

  36. To Summarise + No Residual Sn traces on the sample surface Good Nb3Sn film superconductive properties + Tc = 16,5 K, DTc = 0,3 K + No Sn rich Phases Method: “Hybrid” process

  37. Work in progress • Two furnaces system to avoid air contamination of the superconducting thin film while opening the vacuum system • Use of the best results to coat 6 GHz Nb cavities for a Nb3Sn RF properties sistematic testing • Use of a different experimental method to prepare Nb3Sn: • multilayer obtained altermatively depositing Nb and Sn

  38. Conclusions • Liquid solute diffusion technique (working T > 930 °C) • Three different processes: • “1 step” • “2 steps” • “Hybrid” • trying to optimize T and t • Finally: • ◊ Good superconducting properties • ◊ No Sn • ◊ No Sn rich Phases

  39. End

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