superconducting cavities at 200 mhz fabrication and performance
DESCRIPTION
Superconducting Cavities at 200 MHz Fabrication and Performance. H. Padamsee. Rongli Geng, Enrico Chiaveri and Roberto Losito. 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 - PowerPoint PPT PresentationTRANSCRIPT
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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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