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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 ->large 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-> 300
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First Test Results (Summer 02)
Need to • Reduce field emission• Improve processing
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SEC =2.5
SEC=3.0
Multipacting Simulations
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Re-Rinse at CERN, HPR, Fixed Probe
Epk=17 MV/m
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X-Radiation Levels
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3rd Test Jan 03, long time He processing
Radiation levelStill 30 R
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Q-Slope = Material Property of FilmsDepends on Film Quality and Cu Substrate Also
Nb-Cu
Bulk Nb
1500 MHz
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CERN 350 MHz LEP Cavities
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Q-Slope Decreases with Temperature
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Q-Slope Decreases With Frequency Measured Dependence of Q-Slope
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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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Niobium sputteringNiobium sputtering
Sputtering parameters 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):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
What Next?
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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
Nb
Nb
Cu
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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