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 • Develop large scale cavity fabrication methods
– Need ≈ 600 cells
200 MHz Cavity - Ready for Test
400 mm diameter beam pipe-> 300
First Test Results (Summer 02)
Need to • Reduce field emission• Improve processing
SEC =2.5
SEC=3.0
Multipacting Simulations
Re-Rinse at CERN, HPR, Fixed Probe
Epk=17 MV/m
X-Radiation Levels
3rd Test Jan 03, long time He processing
Radiation levelStill 30 R
Q-Slope = Material Property of FilmsDepends on Film Quality and Cu Substrate Also
Nb-Cu
Bulk Nb
1500 MHz
CERN 350 MHz LEP Cavities
Q-Slope Decreases with Temperature
Q-Slope Decreases With Frequency Measured Dependence of Q-Slope
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
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?
AFM Results on Surface Structure of Nb/Cu
Compare Large and Small Grains
Standard films Oxide-free films
Better Films with Krypton
Large Scale FabricationINFN Spinning 500 MHz Cavity from Tube
Dimension Check
Several Cavities Received
Explore Bias Sputtering Using 500 MHz Cavities
Nb
Nb
Cu
Argon Ion bombardment of Nb film should increase film smoothness
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