Superconducting Cavities at 200 MHz Fabrication and Performance

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Superconducting Cavities at 200 MHz Fabrication
and Performance
H. Padamsee
Rongli Geng, Enrico Chiaveri and Roberto Losito
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Goals

• Extend SRF to 200 MHz -gtlarge scale SC cavities
• Aim for Nb-Cu to cut Nb material cost
• Aim for.. Epk (at surface) 25 - 30 MV/m
• Develop large scale cavity fabrication methods
• Need 600 cells

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200 MHz Cavity - Ready for Test
400 mm diameter beam pipe-gt 300
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First Test Results (Summer 02)
Need to  Reduce field emission  Improve
processing
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Multipacting Simulations
SEC3.0
SEC 2.5
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Re-Rinse at CERN, HPR, Fixed Probe
Epk17 MV/m
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X-Radiation Levels
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3rd Test Jan 03, long time He processing
Radiation level Still 30 R
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Q-Slope Material Property of FilmsDepends on
Film Quality and Cu Substrate Also
Nb-Cu
1500 MHz
Bulk Nb
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CERN 350 MHz LEP Cavities
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Q-Slope Decreases with Temperature
400 MHz LHC Measured
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Q-Slope Decreases With Frequency Measured
Dependence of Q-Slope
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200 MHz, Expected From Temp and Frequency
Dependence
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What Next?
CERN has already built a second Nb-Cu cavity by
the same method. This will test variability in
film properties. Could re-coat with Krypton
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What Next?
Niobium sputtering

• Sputtering parameters
• Discharge current stabilized at 3 A.
• Sputter gas pressure of 1.5x10-3 mbar,
  corresponding to 360 V.
• Coating temperature is 150 C.
• Thickness 1.5 µm
• Film characteristics (same as for LEP)
• RRR 11.5 0.1
• Argon content 435 70 ppm
• Grain size 110 20 nm
• Tc 9.51 0.01 K

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AFM Results on Surface Structure of Nb/Cu
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Compare Large and Small Grains
Standard films
Oxide-free films
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Better Films with Krypton
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Large Scale FabricationINFN Spinning 500 MHz
Cavity from Tube
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Dimension Check
Several Cavities Received
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Explore Bias Sputtering Using 500 MHz Cavities
Argon Ion bombardment of Nb film should increase
film smoothness
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Conclusions

• First ever 200 MHz Nb-Cu Cavity completed
  successfully
• Test facilities ready at Cornell
• First results very encouraging (Eacc 11 M/m
  CW), surface E field 19 MV/m..Goal 25-30 MV/m
• Further work needed to reduce Nb-Cu Q-slope..
• Re-sputter with krypton gas
• Explore Bias magnetron sputtering
• Continue efforts to process to reduce field
  emission
• Spinning of 500 MHz copper cavities from tube
  successful

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