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Atroshchenko - Presence of residual Tin drops in Thermally diffused Nb3Sn


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Presence of Residual Tin drops on Thermally Diffused Nb3Sn (Atroschenko Konstantin - 10')
Speaker: Atroschenko Konstantin - INFN-LNL | Duration: 10 min.

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Atroshchenko - Presence of residual Tin drops in Thermally diffused Nb3Sn

  1. 1. "Presence of residual Tin drops in Thermally diffused Nb3Sn"<br />Authors: Konstantin Atroshchenko<br />Antonio Alessandro Rossi<br />Supervisor: prof. Enzo Palmieri<br />
  2. 2. Liquid tin diffusion is a method of obtaining the superconductive A15 Nb3Sncoating over the 6 GHz cavities or other substrates. A bulk Nb 6 GHz cavity is introduced into molten Sn (dipping step) and after it follows the heat treatment (annealing step). <br />Advantages of the liquid Tin diffusion method <br /><ul><li> relatively cheap technique;
  3. 3. uniformity of the film (stoichiometrically);
  4. 4. can be used for covering surface of wide and complex shaped substrates (!).
  5. 5. we don't need to manipulate dangerous substances as SnCl2to create a nucleation centers, and the diffusion process is considerably faster</li></li></ul><li>6 GHz cavities ready for treatments<br />
  6. 6. Experimental stand<br />linear feedthrough<br /><ul><li> Inconel chamber: (chosen because of its stability at the high process temperature). </li></ul>top chamber<br />flanges<br />pumping<br />cooling <br />water<br />upper furnace<br /><ul><li>Alumina (Al2O3) crucible contains the Sn inside (99.99% nominal purity);</li></ul>cavity<br />lower furnace<br />crucible with liquid Tin<br />
  7. 7. Problems of the method<br />Problem:<br /><ul><li>The residual droplets of Tin on the banded parts (planes, which is horizontal) of the cavity </li></ul>Problem: <br /><ul><li>external furnace. Maximum temperature 1200OC, but it’s hard to transmit it inside the chamber, so the temperature inside is not high enough to evaporate the residual Tin droplets
  8. 8. Diffusion of contaminations through the wall of the chamber at high temperatures</li></ul>external furnace<br />cavity<br />droplets <br />of Tin<br />vacuum chamber<br />
  9. 9. Residual Tin drops on the internal and external surface of the cavity<br />External surface <br />Internal surface <br />Sn<br />Nb3Sn<br />Sn<br />
  10. 10. The L - samples<br />15<br />For the experiment was designed the L-samples, which imitates the shape of the cavity. Samples is made of Niobium. <br />3<br />50<br />10<br />
  11. 11. Basic surface treatment (for all samples)<br />1. Mechanical treatment<br />All samples have been lapped using abrasive papers to reduce the residual roughness after machining.<br />2. Basic chemical treatments<br /><ul><li>washing in Rodaclean with ultrasonic (60 min)
  12. 12. washing in deionized water with ultrasonic
  13. 13. washing with deionized water
  14. 14. drying with nitrogen
  15. 15. BCP in the solution: HF/HNO3/H3PO4 = 1/1/2
  16. 16. washing with deionized water
  17. 17. drying with nitrogen</li></li></ul><li>Preparing the surface. Glow Discharge<br />Procedure:<br />Ultrasonic + Rodaclean 60 min<br />voltage connector<br />feedthrough with the sample inside<br />Clean with acetone<br />chamber<br />baking time: 16 hours;<br />baking temperature 120oC ;<br />GD pressure: 10-3 mBar;<br />Cathode Parameters:<br />current: 0,04 A<br />Coil Parameters:<br />Current : 8 A<br />Magnetic field 525 Gauss<br />Clean with alcohol<br />Glow Discharge 1 min<br />coil<br />Annealing. 4 hours. T = 1000OC<br />
  18. 18. Glow Discharge. Results.<br />Flange<br />Ceramic tube <br />Sample<br />After dipping and annealing<br />@ 1000oC<br />Horizontally fixed sample<br />Nb wire<br />Glow discharge. View from the bottom window<br />After glow discharge<br />
  19. 19. Preparing the surface. Anodization<br />Procedure:<br />Ultrasonic + Rodaclean 60 min<br />sample<br />Clean with acetone<br />Ammonium <br />citrate <br />Clean with alcohol<br />BCP 10 min<br />To the power supply <br />After anodization<br />After dipping and annealing<br />@ 1000oC<br />Anodization in<br />ammonium citrate. V = 20V <br />Annealing. 4 hours. T = 1000OC<br />
  20. 20. Preparing the surface. Chemical etching<br />Procedure:<br />Ultrasonic + Rodaclean 60 min<br />Clean with acetone<br />Clean with alcohol<br />Chemical etching<br />HNO3 : HF = 1 : 1<br />After annealing<br />After etching<br />
  21. 21. Comparison of external resistive and internal heaters<br />
  22. 22. Internal heater high temperature annealing<br />The cross-section of the system:<br />Linear feedthrough<br />L - samples<br />Hot zone<br />heater<br />Cold zone<br />Vacuum chamber<br />Pumping out<br />
  23. 23. Vacuum Chamber<br />Whole – metal valve<br />Vacuum chamber<br />Pumping control unit<br />Gate switch<br />baking control unit<br />Temperature control unit<br />
  24. 24. Comparison of annealing at 1000OC and 1300OC<br />annealing at 1300OC<br />for 5 minutes<br />annealing at 1000OC<br />for 4 hours<br />Just BSP<br />anodization<br />etching<br />glow discharge<br />
  25. 25. Outlook<br /><ul><li> Definition of optimal parameters of high temperature annealing: temperature and time of annealing, ets.
  26. 26. SEM measurements
  27. 27. Profilometric measurements
  28. 28. Covering of the Nb 6 GHz cavities;
  29. 29. RF – measurements</li></li></ul><li>Thank you for attention!<br />
  30. 30. Phase diagram of Nb - Sn<br />
  31. 31. Short theoretical part <br />The theoretical explanation of the process is basis on the Fick’s first law<br />In two or more dimensions we must use the operator, which generalizes the first<br />derivative, obtaining<br />
  32. 32. High – temperature annealing<br /><ul><li>process pressure: 3*10-6 mBar;
  33. 33. time of treatment: 5 min
  34. 34. maximum rf - power: 5 kW
  35. 35. process temperature: 1200 – 1500OC</li></ul>feedthrough (Nb)<br />wave – guide coil<br />samples<br />vacuum chamber<br />sample after annealing<br />
  36. 36. High – temperature annealing heater<br />
  37. 37. Heating of the 6 GHz cavity<br />