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Atroshchenko - Presence of residual Tin drops in Thermally diffused Nb3Sn
 

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 Atroshchenko - Presence of residual Tin drops in Thermally diffused Nb3Sn Presentation Transcript

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