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For superconducting alloys and compounds, at a given operating temperature, the best rf performances (low surface resistance and high relevant critical fields) are obtained for high Tc and low ...

For superconducting alloys and compounds, at a given operating temperature, the best rf performances (low surface resistance and high relevant critical fields) are obtained for high Tc and low resistivity materials. Among the possible candidates, A15 compounds appear to be the most promising.
We needed a fast, easy and performing way to characterize A15 superconducting materials for their potential application to accelerating resonators. The idea is to build microcavities completely equal in shape to the real scale model. The rf characterization of samples is an useful diagnostic tool to accurately investigate local properties of superconducting materials. However, a common limitation of systems used for this, often consists in the diculty of scaling the measured results to the real resonator.
In this work we will proof that 6 GHz resonators can simply become our cavity shaped samples. Our attention was focused on two materials: V3Si that has a really high RRR value and Nb3Sn that is the only A15 material already used for a resonant accelerating structure.
The process parameters optimization necessary to improve the A15 phase superconducting properties, crystal structure and morphology is going on through the small sample production: this is fundamental but still not enough.
We are perfectly aware that having satisfactory results with A15 samples, doesn't mean obtaining good superconducting cavities with ease. Our solution is to work directly with cavities. Obviously using 1.5 GHz resonant structures would be time wasting and a cost limited approach. In the best situation, working very hard, one can produce and measure one resonator every two weeks.
6 GHz cavities are made from larger cavities fabrication remaining material, they don't need welding (even for anges) and they can be directly measured inside a liquid helium dewar. Finally it is possible to perform more than one rf test per day!

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44 deambrosis ph_d_6g_hz cavities_ottim Presentation Transcript

  • 1. For this and many more thesis, visit the free download area on: http://www.surfacetreatments.it/ http://www.slideshare.net/PalmieriProfEnzo
  • 2. Scientific background The International Committee for Future Accelerators recommended that the Linear Collider design has to be based on the superconducting technology new resonant cavity fabrication techniques cost reduction
  • 3. Scientific background Bulk Nb cavities Drawbacks Expensive Low performance at high field Working T = 1.8 K
  • 4. Thesis goal We needed: To pursue research on new materials To efficiently test material SC properties
  • 5. Outline: fundamentals Resonant cavities SC resonant cavities Alternative materials to bulk Nb A15 compounds
  • 6. Outline: experimental 6 GHz cavities Cavity geometry Preliminary surface treatments Cryogenic infrastructure Measuring bench A15 compounds production
  • 7. Outline: experimental A15 compounds production Nb3Sn V3Si Method Method Exp. App. Exp. App. Results Results Samples Samples 6 GHz cavities 6 GHz cavities
  • 8. Cavity fundamentals Prologue 6 GHz To support the cavity electromagnetic fields, Geometry curents flow in the cavity walls at the surface and power Surf. Treat. is dissipated Cryo. Infrastr. 1 2 Pd   RS H ds Measuring 2S bench Nb3Sn Related to the power dissipation, is the cavity quality: 1 step 2 step 0U hybrid Q0  V3Si Pd U is the total (time averaged) energy stored in the cavity Future Dev.
  • 9. Surface Impedance Prologue 6 GHz For a normal metal in the normal regime: cavity Geometry 1 i rn  1  i  Surf. Treat. Zn  s nd d Cryo. Infrastr. Measuring bench where sn = 1 / rn is the dc conductivity at T, d is the penetration depth Nb3Sn 1 step Extension to Superconductors: 2 step hybrid V3Si s1-is2 in place of sn Future Dev.
  • 10. Surface Resistance Prologue 6 GHz cavity As derived by Nam, for T < Tc / 2, Rs can be Geometry approximated by: Surf. Treat. s1 Cryo. Infrastr. Rs 1 sn Measuring bench  3 Nb3Sn Rn 2  2 s2 1 step   2 step sn  hybrid V3Si Future Dev.
  • 11. Mattis and Bardeen integrals Prologue 6 GHz In the framework of the BCS theory, for ћ < 2 , the complex cavity conductivity of a superconductor is: Geometry  s1 2  f  E   f  E   g   E  dE     Surf. Treat. sn  Cryo.  Infrastr. s2 1 1  2 f  E   g   E  dE    ,    Measuring sn  bench Nb3Sn 1 step 2 step Being: 2  skBTc hybrid V3Si f E   1 E 2  2  E g E    1  e  E / k BT   E 2  2  E    2  2 Future Dev.
  • 12. Mattis and Bardeen integrals Prologue 6 GHz The two integrals s1/sn and s2/sn are easily numerically calculated. cavity In the normal skin effect regime, for ħ << 2  Geometry  2  s 2   Surf. Treat. s1   K BT   e  / K BT ln   tanh s n  1  e / K BT 2   sn  2 K BT Cryo.     Infrastr. Measuring bench Nb3Sn 1 step 2 step hybrid V3Si Future Dev.
  • 13. BCS Surface Resistance Prologue 6 GHz cavity Then, if T < Tc / 2 Geometry 3  Surf. Treat. Rn    s 1  1  O, , T  2 RBCS     A rn e k BT 2    s n Cryo. Infrastr. 1/ 2 Measuring  21  K  3 with A  6.0  10  4  bench  ms  Nb3Sn 1 step 2 step But R S (T )  RBCS (T )  R0 hybrid V3Si Empirically, R0 is found to be dependent on rn too. Future Dev.
  • 14. Selection criteria Prologue 6 GHz cavity Geometry For low rf losses, Surf. Treat. a high Tc value is not sufficient Cryo. Infrastr. Measuring bench A metallic behaviour Nb3Sn in the normal state is 1 step 2 step mandatory hybrid V3Si Future Dev.
  • 15. A15 materials Prologue B A 6 GHz cavity  Cubic crystal structure Geometry (W3O or Cr3Si type) Surf. Treat.  Stoichiometric Cryo. composition A3B Infrastr. Measuring bench  B —> bcc crystal Nb3Sn structure 1 step 2 step  A —> chains parallel to the three directions hybrid [100], [010], [001] V3Si  LRO Future Dev.
  • 16. A15 materials Prologue 6 GHz cavity Geometry Surf. Treat. Cryo. Infrastr. Measuring bench Nb3Sn 1 step 2 step hybrid V3Si Future Dev.
  • 17. A15 materials Prologue 6 GHz cavity Geometry A15 chosen for rf applications : Surf. Treat. Cryo. Infrastr. Nb3Sn —> Tc = 18,3 K, ρn ≈ 10 μΩcm Measuring bench Nb3Sn V3Si —> Tc = 17,1 K, ρn ≈ 10 μΩcm 1 step 2 step hybrid V3Si Future Dev.
  • 18. Nb3Sn Prologue Nb3Sn nomogram (f = 500 MHz, T = 4.2 K, s = 4). ρn ≈ 10 μΩcm is possible 6 GHz and Tc = 18.0 K: the ideal RBCS value could be lower than 1 nΩ. cavity Geometry Surf. Treat. Cryo. Infrastr. ρn (μΩcm) Measuring bench Nb3Sn ~ 10 Ideal μΩcm RBCS ~ 1 nΩ 1 step 2 step hybrid V3Si 18 Future Tc (K) Dev.
  • 19. V3Si Prologue V3Si nomogram (f = 500 MHz, T = 4.2 K, s = 4). ρn ≈ 10 μΩcm is possible and 6 GHz Tc = 17.1 K: the ideal RBCS value could be as low as 1 nΩ. cavity Geometry Surf. Treat. Cryo. Infrastr. ρn (μΩcm) Measuring bench Nb3Sn ~ 10 Ideal μΩcm RBCS ~ 1 nΩ 1 step 2 step hybrid V3Si 18 Future Tc (K) Dev.
  • 20. UNIVERSITA’ DEGLI STUDI DI PADOVA Scuola di Dottorato in Scienza ed Ingegneria dei Materiali PhD Thesis 6 GHz cavities: A method to test A15 intermetallic compounds rf properties Silvia M. Deambrosis
  • 21. Surface Resistance measurement Prologue 6 GHz Methods to measure a superconductor surface resistance: cavity Geometry • Ring microstrip resonator technique Surf. Treat. • Niobium triaxial cavity • Vacuum insulated termometers Cryo. Infrastr. Measuring bench Nb3Sn 1 step 2 step hybrid V3Si Future Dev.
  • 22. Surface Resistance measurement Prologue 6 GHz Methods to measure a superconductor surface resistance: cavity Geometry • Ring microstrip resonator technique Surf. Treat. • Niobium triaxial cavity • Vacuum insulated termometers Cryo. Vacuum Infrastr. port Electrical feedthrough Measuring Therm. bench chamber Nb3Sn In seal 1 step T sensors 2 step gap hybrid Sample Triaxial cavity V3Si Future Dev.
  • 23. Surface Resistance measurement Prologue 6 GHz Methods to measure a superconductor surface resistance: cavity Geometry • Ring microstrip resonator technique Surf. Treat. • Niobium triaxial cavity • Vacuum insulated termometers Cryo. Infrastr. Measuring bench Nb3Sn 1 step 2 step hybrid V3Si Future Dev.
  • 24. Surface Resistance measurement Prologue 6 GHz Methods to measure a superconductor surface resistance: cavity Geometry • Ring microstrip resonator technique Surf. Treat. • Niobium triaxial cavity • Vacuum insulated termometers Cryo. Infrastr. Measuring bench Pro and Con Nb3Sn + 1 step Useful diagnostic tool to accurately investigate local 2 step properties of superconducting materials hybrid V3Si - Difficulty of scaling the measured results to a real resonator Future Dev.
  • 25. 6 GHz cavities Prologue 6 GHz cavities 6 GHz cavity Geometry Seamless: no welding (neither for flanges) Surf. Treat. Obtained from scrap Nb (Low cost) Cryo. 10 min fabrication time Infrastr. Easy BCP and EP treatments (small acid quantity) Measuring bench Inexpensive Cryogenics Nb3Sn Quick RF Measurements (He dewar) 1 step 2 step For testing hybrid rf SC properties V3Si NO SAMPLE IS COMPARABLE TO A CAVITY! Future Dev.
  • 26. Cavity geometry Prologue 10 6 GHz mm cavity Geometry Surf. Treat. 93 mm Cryo. Infrastr. Measuring bench Nb3Sn 1 step 25 2 step mm hybrid V3Si Future Dev.
  • 27. Nb 6 GHz cavities Prologue 6 GHz cavity Internal surface: Geometry  bad finishing  contaminants Surf. Treat. Cryo. Infrastr. Measuring Treatments: bench Nb3Sn 1 step 2 step hybrid V3Si Future Dev.
  • 28. Nb 6 GHz cavities Prologue 6 GHz cavity Internal surface: Geometry  bad finishing SiC ZrO2 Al2O3 + SiO2  contaminants Surf. Treat. Cryo. Infrastr. Measuring Treatments: bench  Mechanical Nb3Sn 1 step 2 step hybrid V3Si Future Dev.
  • 29. Nb 6 GHz cavities Prologue 6 GHz cavity Internal surface: Geometry  bad finishing  contaminants Surf. Treat. Cryo. Infrastr. Measuring Treatments: bench  Mechanical Nb3Sn  Thermal 1 step 2 step hybrid V3Si Future Dev.
  • 30. Nb 6 GHz cavities Prologue 6 GHz cavity Internal surface: Geometry  bad finishing  contaminants Surf. Treat. Cryo. Infrastr. Measuring Treatments: bench  Mechanical Nb3Sn  Thermal HF, HNO3, H3PO4 1 step  BCP 1:1:2 2 step hybrid V3Si Future Dev.
  • 31. Nb 6 GHz cavities Prologue 6 GHz cavity Nitric acid oxidizes the Nb surface Geometry 6 Nb( s )  10 HNO3( aq )  3Nb2O5( s )  10 NO( g )  5H 2O(l ) Surf. Treat. Cryo. Hydrofluoric acid reduces the Nb2O5 into a soluble salt Infrastr. Measuring 1 3 Nb2O5( s )  6 HF( aq )  H 2 NbOF5( aq )  NbO2 F  H 2O  H 2O(l ) bench 2 2 Nb3Sn 1 3 NbO2 F  H 2O  4 HF( aq )  H 2 NbOF5( aq )  H 2O(l ) 1 step 2 2 2 step hybrid V3Si Phosphoric acid acts as a moderator Future Dev.
  • 32. Nb 6 GHz cavities Prologue 6 GHz cavity Internal surface: Geometry  bad finishing  contaminants Surf. Treat. Cryo. Infrastr. Measuring Treatments: bench  Mechanical Nb3Sn  Thermal 1 step  BCP 2 step  EP hybrid V3Si HF, H2SO4 Future 1:9 Dev.
  • 33. Nb 6 GHz cavities Prologue 6 GHz SiC 36h + ZrO2 96h + Al2O3-SiO2 48h ZrO2 108h cavity Geometry Surf. Treat. Cryo. Infrastr. Measuring bench BCP 1h EP 2h Nb3Sn 1 step 2 step hybrid V3Si Future Dev.
  • 34. V 6 GHz cavities Prologue 6 GHz cavity Geometry Surf. Treat. Cryo. Infrastr. Measuring After: bench Before the treatment SiC 120h + ZrO2 96h Nb3Sn 1 step 2 step hybrid V3Si Future Dev.
  • 35. Cryogenic infrastructure Prologue 6 GHz cavity Geometry Surf. Treat. Cryo. Infrastr. Measuring bench Nb3Sn 1 step 2 step hybrid V3Si Future Dev.
  • 36. Cryogenic infrastructure Prologue 6 GHz cavity Geometry Surf. Treat. Cryo. Infrastr. Measuring bench Nb3Sn 1 step 2 step hybrid V3Si Future Dev.
  • 37. Cryogenic infrastructure Prologue 6 GHz cavity Geometry Surf. Treat. Cryo. Infrastr. Measuring bench Nb3Sn 1 step 2 step hybrid V3Si Future Dev.
  • 38. Cryogenic infrastructure Prologue The bottom part is completely independent 6 GHz cavity Geometry Surf. Treat. Cryo. Infrastr. Measuring bench Nb3Sn 1 step 2 step hybrid V3Si Future Dev.
  • 39. Measuring bench Prologue The insert has been conceived to enter a 450 l dewar neck 6 GHz cavity Geometry Surf. Treat. Cryo. Infrastr. Measuring bench Nb3Sn 1 step 2 step hybrid V3Si Future Dev.
  • 40. rf System schematic Prologue 6 GHz cavity Geometry Surf. Treat. Cryo. Infrastr. Measuring bench Nb3Sn 1 step 2 step hybrid V3Si Future Dev.
  • 41. rf Chassis Prologue The rf system works at three different frequency ranges: 6 GHz 160 MHz, 1.3-1.5 GHz, 6 GHz cavity Geometry Surf. Treat. Cryo. Infrastr. Measuring bench Nb3Sn 1 step 2 step hybrid V3Si Future Dev.
  • 42. VCO-PLL Prologue 6 GHz The VCO-PLL enable us to lock the resonant cavity cavity Geometry Surf. Treat. Cryo. Infrastr. Measuring bench Nb3Sn 1 step 2 step hybrid V3Si Future Dev.
  • 43. Nb 6 GHz cavities Prologue Example: the same cavity has been surface treated (BCP + EP) and 6 GHz rf tested more than once cavity Geometry Surf. Treat. Q Cryo. Infrastr. Measuring bench Nb3Sn 1 step 2 step hybrid V3Si Eacc (V/m) Future Dev.
  • 44. Outline: experimental A15 compounds production Nb3Sn V3Si Method Method Exp. App. Exp. App. Results Results Samples Samples 6 GHz cavities 6 GHz cavities
  • 45. Nb3Sn: Liquid Sn diffusion Prologue 6 GHz Nb3Sn can be obtained using different techniques: cavity Geometry  Bronze Process,  Vapor Sn diffusion (Wuppertal), Surf. Treat.  Liquid Sn Diffusion Cryo. Infrastr. Measuring bench Bulk Nb substrate Nb3Sn Dipping in a liquid Sn bath Annealing 1 step 2 step hybrid • No nucleation sites on Nb are required V3Si • Fast growth of Nb3Sn layer Future Dev.
  • 46. Nb3Sn: experimental apparatus Prologue 6 GHz cavity Geometry Linear feedtrough Surf. Treat. Cryo. Infrastr. Cooling water jacket Measuring bench Furnace Nb3Sn Furnace 1 step 2 step Liquid Sn hybrid V3Si Future Dev.
  • 47. Nb3Sn: phase diagram Prologue 6 GHz cavity Geometry Nb3Sn Surf. Treat. Cryo. Infrastr. Measuring bench 930°C Nb3Sn 1 step 2 step < Tc hybrid phases V3Si Future Dev.
  • 48. Nb3Sn: different methods Prologue 6 GHz cavity Geometry Now: 1 step 2 step Hybrid Surf. Treat. Cryo. Infrastr. Sn vapor Vacuum Sn vapor Annealing Measuring Annealing Annealing + bench Vacuum Annealing Nb3Sn • residual Sn • low Tcs 1 step • spurious phases • spurious phases 2 step Good Tcs, hybrid No residual Sn, V3Si No spurious phases Future Dev.
  • 49. Nb3Sn “1 step”: SEM Prologue Proc T = 1000°C, Dipp t = 120’, Ann t = 14h 6 GHz cavity Geometry Surf. Treat. Cryo. Infrastr. Measuring bench Nb3Sn 1 step 2 step hybrid V3Si Future Dev.
  • 50. Nb3Sn “1 step”: SEM Prologue 6 GHz cavity Proc T = 1050°C Proc T = 1050°C Dipp t = 120’ Dipp t = 120’ Geometry Ann t = 14h Ann t = 22h Surf. Treat. Cryo. Infrastr. Measuring bench Proc T = 1050°C Nb3Sn Dipp t = 120’ Ann t = 14h 1 step (T = 1050°C) 2 step + hybrid 5h (T = 500°C) V3Si Future Dev.
  • 51. Nb3Sn “1 step”: XRD Prologue 6 GHz cavity Process T = 1000°C, Dipping t = 30’, Annealing t = 10h Geometry Surf. Treat. Relative Intensity Dipping T = 1000 °C Cryo. Dipping t = 30 min Infrastr. Annealing T = 1000 °C Measuring Annealing t = 10 h bench Nb3Sn 1 step 2 step hybrid V3Si Angle 2θ (degrees) Future Dev.
  • 52. Nb3Sn “1 step”: PPMS Prologue 6 GHz Proc T = 1000°C, Dipp t = 120’, Ann t = 14h (1000°C) + 5h (T = 500°C) cavity Geometry Surf. Treat. Cryo. Infrastr. Measuring bench Nb3Sn 1 step 2 step hybrid V3Si Future Dev.
  • 53. Nb3Sn “1 step”: EMPA Prologue Proc T = 1000°C, Dipp t = 120’, Ann t = 14h (1000°C) + 5h (T = 500°C) 6 GHz cavity Geometry Surf. Treat. Cryo. Infrastr. Measuring bench Nb3Sn 1 step 2 step hybrid V3Si Future Dev.
  • 54. 1-step process Summary + Nb3Sn with good superconductive properties Tc max= 17,7 K Tc= 0,1 K - Residual Sn traces on the sample surface - Sn rich Phases Presence
  • 55. Nb3Sn “2 step”: SEM Prologue Proc T = 1025°C, Dipp t = 15’, Ann t = 15h 6 GHz cavity Geometry Surf. Treat. Cryo. Infrastr. Measuring bench Nb3Sn 1 step 2 step hybrid V3Si Future Dev.
  • 56. Nb3Sn “2 step”: XRD Prologue 6 GHz cavity I Proc T = 1025°C, Dipp t = 5’, Geometry Ann t = 20 h Surf. Treat. Cryo. Infrastr. Measuring I bench Proc T = 1025°C, Dipp t = 5’, Nb3Sn Ann t = 10 h 1 step 2 step hybrid V3Si 2Θ ( ) Future Dev.
  • 57. Nb3Sn “2 step”: PPMS Prologue Dipp T = 1025°C, Dipp t = 30’, Ann T = 1000°C, Ann t = 10h 6 GHz cavity Geometry Surf. Treat. Tc = 16.6 K ΔTc = 0.32 K Cryo. Infrastr. Measuring bench Nb3Sn 1 step 2 step hybrid V3Si Future Dev.
  • 58. Nb3Sn “2 step”: PPMS Prologue Same recipe except for the annealing temperature 6 GHz cavity Geometry Dipp T = 1025°C, Dipp t = 30’, Surf. Treat. Ann t = 10h Cryo. Infrastr. Measuring bench Nb3Sn 1 step 2 step hybrid V3Si Future Dev.
  • 59. Nb3Sn “2 step”: PPMS Prologue Same recipe except for the annealing time 6 GHz cavity Geometry Surf. Treat. Cryo. Dipp T = 1025°C, Dipp t = 5’, Ann T = 1050°C Infrastr. Dipp T = 975°C, Dipp t = 30’, Ann T = 975°C Measuring bench Nb3Sn 1 step 2 step hybrid V3Si Future Dev.
  • 60. Nb3Sn “2 step”: PPMS Prologue Sample 37 superconducting properties: Tc = 16.9 K, Tc = 0.1 K 6 GHz 8 twin samples: they have been treated with an HCl solution in cavity different conditions Geometry Surf. Treat. Cryo. Infrastr. Measuring bench Nb3Sn 1 step 2 step hybrid V3Si Future Process T (°C) Dev.
  • 61. Nb3Sn 6 GHz cavities Prologue 6 GHz cavity Nb3Sn 1 Geometry Surf. Treat. Cryo. Infrastr. 1) As obtained Measuring 2) HCl bench 3) HCl + us Nb3Sn 1 step 2 step hybrid V3Si Future Dev.
  • 62. 2-step process Summary + No Residual Sn traces on the sample surface - Worst Nb3Sn film superconductive properties Average Tc = 15,2 K, Tc = 0,5 K - Sn rich Phases Presence - HCl chemical treatment deteriorates the growth film
  • 63. Nb3Sn “hybrid”: XRD Prologue 6 GHz Proc T = 975°C, Dipp t = 30’, Ann (Sn) t = 2h, Ann t = 5h cavity Geometry Surf. Treat. Relative Intensity Cryo. Infrastr. Measuring bench Nb3Sn 1 step 2 step hybrid V3Si Angle 2θ (degrees) Future Dev.
  • 64. Nb3Sn “hybrid”: PPMS Prologue 6 GHz Proc T = 975°C, Dipp t = 30’, Ann (Sn) t = 2h, Ann t = 2h cavity Geometry Surf. Treat. Tc = 16.8 K Cryo. ΔTc = 0.16 K Infrastr. Measuring bench Nb3Sn 1 step 2 step hybrid V3Si Future Dev.
  • 65. Nb3Sn 6 GHz cavities Prologue 6 GHz cavity Geometry Surf. Treat. Cryo. Infrastr. Measuring bench Nb3Sn 1 step 2 step hybrid V3Si Future Dev.
  • 66. Hybrid process Summary + No Residual Sn traces on the sample surface Good Nb3Sn film superconductive properties + Tc max = 16,9 K, Tc = 0,15 K + No Sn rich Phases
  • 67. Outline: experimental A15 compounds production Nb3Sn V3Si Method Method Exp. App. Exp. App. Results Results Samples Samples 6 GHz cavities 6 GHz cavities
  • 68. V3Si: Thermal diffusion Prologue V3Si can be obtained using different techniques: 6 GHz cavity  Bronze Process, Geometry  PVD, Surf. Treat.  Thermal diffusion (SiH4 decomposition) Cryo. Infrastr. Bulk V substrate Measuring bench 1 • SiH4 Decomposition Nb3Sn • Si Diffusion • V3Si Nucleation 1 step 2 step 2 • Recrystallization hybrid • Film Growing V3Si • H2 Removal Future Variables: T, t, p(SiH4) Dev.
  • 69. V3Si: Thermal diffusion Prologue 6 GHz cavity Geometry • Very simple technique (RF applications!) Surf. Treat. Cryo. Infrastr. • Promising old results Measuring bench Nb3Sn 1 step 2 step hybrid V3Si Future Dev.
  • 70. V3Si: Thermal diffusion Prologue 6 GHz cavity Geometry • Very simple technique (RF applications!) Surf. Treat. Cryo. Infrastr. • Promising old results Measuring bench Nb3Sn • There is room to improve the film quality by > 1 step thermal diffusion temperature or by > annealing 2 step hybrid time in vacuum. V3Si Future Dev.
  • 71. V3Si: heating system Prologue 6 GHz cavity Geometry Surf. Treat. Cryo. Infrastr. Measuring bench Nb3Sn 1 step 2 step hybrid Nb V3Si V substrates Future Dev.
  • 72. V3Si: substrate chemical etching Prologue 6 GHz Erosion cavity Sample Reactant mixture T (°C) t (s) rate Geometry Surf. Treat. Cryo. Infrastr. Measuring bench Nb3Sn 1 step 2 step hybrid V3Si Future Dev.
  • 73. V3Si: substrate chemical etching Prologue 6 GHz cavity Geometry Surf. Treat. Cryo. HF, HNO3, H3PO4 1:1:2 HF, HNO3 1:4 Infrastr. 50°C, 7,8 mm 20°C, 73,8 mm Measuring bench Nb3Sn 1 step 2 step hybrid V3Si HF, HNO3, H3PO4 1:1:1 HNO3, H2O, NH4F 25:12:1 60°C, 36,2 mm 30°C, 46,5 mm Future Dev.
  • 74. V3Si: SEM Prologue 6 GHz p(SiH4) = 5x10-4 mbar, SiH4 t = 10h, ann t = 20h, process T = 900°C cavity Geometry Surf. Treat. Cryo. Infrastr. Measuring bench Nb3Sn 1 step 2 step hybrid V3Si Future Dev.
  • 75. V3Si: SEM Prologue p(SiH4) = 5x10-3 mbar, SiH4 t = 4h, ann t = 6h, process T = 850°C 6 GHz cavity Geometry Surf. Treat. Cryo. Infrastr. Measuring bench Nb3Sn 1 step 2 step hybrid V3Si Future Dev.
  • 76. V3Si: EDX Prologue 6 GHz p(SiH4) = 5x10-4 mbar, SiH4 t = 10h, ann t = 20h cavity Geometry Surf. Treat. 4F 4N Cryo. Infrastr. 3F Measuring bench Nb3Sn 3N 1 step 2-6N 2 step hybrid V3Si Future Dev.
  • 77. V3Si: EDX Prologue 6 GHz p(SiH4) = 5x10-3 mbar, SiH4 t = 4h, T = 850°C cavity Geometry 12N Surf. Treat. 6N Cryo. Infrastr. Measuring bench Nb3Sn 1 step 2 step 8N 9N hybrid V3Si Future Dev.
  • 78. V3Si: XRD Prologue p(SiH4) = 5x10-4 mbar, SiH4 t = 10h, ann t = 20h, process T = 850°C 6 GHz cavity Geometry Surf. Treat. Cryo. Infrastr. Measuring bench Nb3Sn 1 step 2 step hybrid V3Si Future Dev.
  • 79. V3Si: XRD Prologue p(SiH4) = 5x10-4 mbar, SiH4 t = 10h, ann t = 20h, process T = 900°C 6 GHz cavity Geometry Surf. Treat. Cryo. Infrastr. Measuring bench Nb3Sn 1 step 2 step hybrid V3Si Future Dev.
  • 80. V3Si: XRD Prologue 6 GHz cavity p(SiH4) = 5x10-3 mbar, SiH4 t = 4h, ann t = 16h, process T = 850°C Geometry Surf. Treat. Cryo. Infrastr. Measuring bench Nb3Sn 1 step 2 step hybrid V3Si Future Dev.
  • 81. V3Si: PPMS Prologue 6 GHz p(SiH4) = 1x10-3 mbar, SiH4 t = 10h, ann t = 20h, process T = 850°C cavity Geometry Surf. Treat. Tc = 15.4 K Cryo. ΔTc = 0.23 K Infrastr. Measuring bench Nb3Sn 1 step 2 step hybrid V3Si Future Dev.
  • 82. V3Si: PPMS Prologue 6 GHz p(SiH4) = 5x10-3 mbar, SiH4 t = 4h, ann t = 8h, process T = 850°C cavity Geometry Surf. Treat. Tc = 15.7 K Cryo. ΔTc = 0.2 K Infrastr. Measuring bench Nb3Sn 1 step 2 step hybrid V3Si Future Dev.
  • 83. V3Si: PPMS Prologue p(SiH4) = 5x10-4 mbar, SiH4 t = 10h, ann t = 20h 6 GHz cavity p(SiH4)=5,0 x 10-4mbar, silanization t=10h, ann t=20h Geometry Surf. Treat. Cryo. Infrastr. Tc (°C) Tc (K) Measuring bench Nb3Sn 1 step 2 step hybrid V3Si Process T (°C) Future Dev.
  • 84. V3Si: PPMS Prologue 6 GHz p(SiH4) = 5x10-3 mbar, SiH4 t = 4h, process T = 850°C cavity Geometry Surf. Treat. Cryo. Infrastr. Measuring bench Tc (K) Nb3Sn 1 step 2 step hybrid V3Si Annealing t (h) Future Dev.
  • 85. V 6 GHz cavities Prologue 6 GHz p(SiH4) = 5x10-3 mbar, SiH4 t = 4h, process T = 850°C cavity Geometry Surf. Treat. Cryo. tann = 74h Infrastr. Measuring tann = 36h bench Nb3Sn tann = 12h 1 step 2 step hybrid V3Si Future Dev.
  • 86. V3Si Summary • Thermal diffusion technique •T, t and p(SiH4) change trying to improve V3Si film properties • Good preliminary results: Tc > 16 K and Tc < 0,3 K
  • 87. Nb3Sn - Future plan Prologue Double Furnace System 6 GHz cavity Geometry Built to avoid air contamination of the superconducting thin film while Surf. Treat. opening the vacuum system Cryo. Infrastr. Measuring bench Annealing Furnace Nb3Sn 1 step 2 step hybrid Dipping Furnace V3Si Future Dev.
  • 88. V3Si - Future plan Prologue Thermal Diffusion + Plasma 6 GHz cavity Lamps on Geometry Surf. Treat. Plasma on Cryo. Infrastr. Measuring Electrode bench Nb3Sn V substrates 1 step 2 step hybrid V3Si Future Dev.
  • 89. Nb3Sn 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 • Double furnace system
  • 90. V3Si Conclusions • Thermal diffusion technique • T, t and p(SiH4) change trying to improve V3Si films properties • Good preliminary results: Tc > 16 K and Tc < 0,3 K • Thermal diffusion + Plasma
  • 91. 6 GHz cavities • 80 cavities are under fabrication using Scrap Nb • Flanges are seamless: no brazing, no EB welding • It is possible to perform more than one RF test a day End NO SAMPLE IS COMPARABLE TO A CAVITY!
  • 92. Cavity fundamentals Prologue 6Ghz cavity rf testing Nb3Sn V3Si The accelerating voltage and field are given by: z d Vacc  i 0 z / c Vacc  E z ( z )e dz Eacc  Conclusions z 0 d d = cavity length
  • 93. Cavity fundamentals When considering the limitations of superconducting cavities: Resonant cavities E pk H pk Peak electric surface field Peak magnetic surface field irises equator SC Res. Cav. Field emission danger H pk  H crf Alternative They determine the maximum achievable accelerating gradient material to bulk Nb To maximize the potential cavity performance, the ratios: A15 E pk H pk compounds Eacc Eacc rf testing Must be minimized
  • 94. Cavity fundamentals To support the electromagnetic fields, curents flow in the cavity walls at the surface and power is dissipated Resonant cavities 1 2 Pd   RS H ds 2S SC Res. Cav. Related to the power dissipation, is the cavity quality: 0U Q0  Alternative Pd material to bulk Nb U is the total (time averaged) energy stored in the cavity A15 compounds 1 2 1 2 U  m 0  H dv   0  E dv rf testing 2 V 2 V
  • 95. Cavity fundamentals BCS theory: Resonant • Cooper pairs: two electrons of opposite momentum and spin cavities • Pairing process assisted by phonons SC When 0 < T < Tc Res. Cav. not all the electrons are in the bosonic ground state Alternative If T < Tc/2 material to bulk Nb A15   (T )  ne  2ns T  0  exp   compounds  k T    B  rf testing
  • 96. Cavity fundamentals Can the unpaired electrons be scattered and dissipate Resonant energy? cavities DC case SC Normal conducting electrons never see an electric field Res. Cav. and don’t contribute to the current flow (Cooper pairs “shorts out” any field in the superconductor) Alternative material to bulk Nb RF case Super-electrons no longer screen externally applied fields A15 compounds and normal conducting electrons are accelerated rf testing
  • 97. Cavity fundamentals Can rf cavities operate up to Hpk > Hc1 (type II) or Hc (type I)? Resonant • True for Type I cavities The hypothesis is: H rf c  H sh superconductors • Experiments confirmed Nb Hcrf ≈ Hsh SC Res. Cav. Peak SRF Magnetc Field (mT) Alternative Pulsed rf fields material to 0.5Tc  T  Tc bulk Nb A15 compounds rf testing (T/Tc )2
  • 98. A15 materials Resonant cavities SC Res. Cav. Alternative material to bulk Nb A15 compounds rf testing
  • 99. Nb3Sn “2 step”: SIMS Prologue 6 GHz cavity Proc T = 1025°C, Dipp t = 5’, Geometry Ann t = 10 h Surf. Treat. Proc T = 1025°C, Cryo. Dipp t = 5’, Infrastr. Ann t = 20 h Measuring bench Nb3Sn 1 step 2 step hybrid V3Si Future Dev.
  • 100. V3Si: SEM Prologue 6 GHz p(SiH4) = 5x10-3 mbar, sil t = 4h, ann t = 16h, process T = 850°C cavity Geometry Surf. Treat. Cryo. Infrastr. Measuring bench Nb3Sn 1 step 2 step hybrid V3Si Future Dev.
  • 101. V3Si: SEM Prologue 6 GHz p(SiH4) = 5x10-4 mbar, sil t = 10h, ann t = 20h, process T = 870°C cavity Geometry Surf. Treat. Cryo. Infrastr. Measuring bench Nb3Sn 1 step 2 step hybrid V3Si Future Dev.
  • 102. 6 GHz - Future plan Prologue Atmospheric Plasma 6 GHz cavity Niobium 6 GHz cavity @ 4.2 K Geometry Surf. Treat. Cryo. Infrastr. Measuring bench Nb3Sn 1 step 2 step hybrid V3Si Future Dev.
  • 103. 6 GHz - Future plan Prologue Atmospheric Plasma 6 GHz cavity Niobium 6 GHz cavity @ 4.2 K Geometry Surf. Treat. Cryo. Infrastr. Measuring bench Nb3Sn 1 step 2 step hybrid V3Si Future Dev.
  • 104. 6 GHz - Future plan Prologue Atmospheric Plasma 6 GHz cavity What’s exactly happening? Geometry Surf. Treat. • Desorption of adsorbed gases Cryo. Infrastr. Measuring • Oxidation of C contamination to CO2 bench Nb3Sn • Light baking (50°c 10’) limited to the cell 1 step 2 step hybrid • Enhanced ultrasonic cleaning due to the V3Si superhydrophilic Nb surface Future Dev.
  • 105. Conclusions We Just started, why should we conclude? Better call it: SUMMARY •Vacuum Plasma etching: Nb Removal Rate of tenths of mm/hr, but it can be increased ATMOSPHERIC PLASMA CLEANING: Three Configurations: • Corona Discharge • Plasma Jet • Resonant Plasma 60 min of Atmospheric Plasma Cleaning is beneficial for Q-value Atmospheric Plasma make the Nb surface hydrophylic and prepare it for the following Rinsing
  • 106. For this and many more thesis, visit the free download area on: http://www.surfacetreatments.it/ http://www.slideshare.net/PalmieriProfEnzo