Proof of Principle cavity preparation and testing: ODU/SLAC RF–Dipole Design

1. Joint LARP CM20 / HiLumi Meeting – Napa, CA 8-10 April, 2013 Proof of Principle cavity preparation and testing: ODU/SLAC RF–Dipole Design

2. Proof of Principle Design • Design requirements • Frequency = 400 MHz • Beam aperture = 84 mm • Total transverse voltage = 10 MV • Transverse voltage per cavity = 3.4 MV • Transverse electric and magnetic fields • Surface electric and magnetic fields

3. Basic Properties • No lower order modes • Separation of HOMs from fundamental mode ~ 190 MHz 17 cm 52.8 cm 8.4 cm HOM Properties

4. Fabrication Fine grain Nb – RRR 353-405 Cavity thickness – 3 mm

5. Fabrication • End plates with brazed stainless steel flanges • Center shell formed in two halves • Finished cavity shipped to ODU –March, 2012

6. Bead Pull Study • On-axis transverse electric field was measured using a Teflon bead • Both on-axis transverse electric and magnetic fields were measured using an Al metallic bead

7. Optical Inspection • All the welding seams were inspected ~ 180 images • Grain boundaries • Weld seam

8. Surface Treatment, Preparation and Testing HPR Cabinet BCP Cabinet • Bulk BCP – 85 μm • Heat treatment – At 6000 C for 10 hours • Light BCP – ~10 μm • High Pressure Rinse – 3 passes • Assembly in the clean room • RF Test Plan • High power tests at 2 K and 4 K • Rs vs. T • Pressure test • Lorentz detuning • No He processing was done • RF Tests Performed • 2 K high power test • Cavity warmed up to 4 K • 4 K high power test • Cavity cooled down to 2 K • 2 K high power test

9. Chemical Processing Bulk BCP • Planned total removal – 120 μm • Acid mixture was contaminated with glycol • Reduced etch rate from 2.7-2.8 μm /min to 1.8 μm/min • Average removal 85 microns • Average removal in edges > 90 μm • Average removal on flat surfaces < 70 μm Light BCP • Removal of 10 μm after heat treatment O1 O10 99 μm 81 μm O2 O11 O8 O12 O3 O13 O4 71 μm 63 μm 68 μm O14 O5 O9 O6 O15 95 μm 108 μm O7 O16

10. Heat Treatment At 6000C – 10 hours H2 T = 6000C

11. Assembly • Followed by a HPR of 3 passes • Ultrasonic degreased hardware • Leak tested • Assembly in clean room

12. Preparation for Test • Cable calibration • Q1 = 2.76×109 • Q2= 8.62×1010 • LLRF control • Test with 500 W rf amplifier

13. Design Specifications in Operation • Basic Properties • Required fields

14. Multipacting Analysis Multipacting analysis was done using the Track3P in SLAC – ACE3P suite • A multipacting barrier was observed in the first 2 K test at very low fields • Increasing the power readily processed the cavity • No multipacting was observed in the following 4.2 K and 2 K tests

15. Expected Q0 = 1.6×109 At RS = 90 nΩ And Rres = 20 nΩ Achieved Q0= 1.25×109 Achieved fields ET = 11.6 MV/m VT = 4.35 MV EP = 47 MV/m BP = 82 mT Limited by rf power 4.2 K Test Results 3.4

16. Rsvs T, Pressure Test, Lorentz Detuning • Frequency deviations • Room temperature f : 402.0 MHz • After bulk BCP : Δ f =  51.1 kHz • After bake : Δ f=  30.2 kHz • Under vacuum : Δf= 318.5 kHz • At 2 K : Δf= 365.3 kHz RS = 34 nΩ

17. 2 K Test Results Expected Q0 = 6.7×109 At RS = 22 nΩ And Rres = 20 nΩ Achieved Q0= 4.0×109 Achieved fields ET = 18.6 MV/m VT = 7.0 MV EP = 75 MV/m BP = 131 mT Quench 3.4 5.0

18. Field Emission

19. Summary • Proof-of-Principle cavity achieved 7 MV deflecting voltage cw • Residual surface resistance a little high (34 nΩ) • Possibly due to contaminated acid, not enough Nbremoved • Consistent with losses in stainless steel flanges and copper probes in coupler ports • Multipacting quickly processed and did not reoccur • Proof-of-Principle cavity has achieved its purpose • Ready to move on to the prototype cavity • Reasonably confident that 10 MV can be achieved with 2 cavities

20. Acknowledgements • ODU • Chris Hopper • Alex Castilla • HyeKyoung Park • SLAC • Zenghai Li • Niowave • Terry Grimm • Dmitry Gorelov • Chase Boulware • Nick Miller • JLab • HyeKyoung Park • Peter Kneisel • RongliGeng • Joe Preble • Tony Reilly • Tom Powers • Kirk Davis • Pete Kushnick • Danny Forehand and his team • Steve Castagnola and his team • Dave McCay • Casy Apeldoorn