1. Experiences with KEK-B Crab Cavity KEKB and Crab Cavity History of Crab Cavity Construction and Operation of KEKB Crab Cavities What the KEKB Crab Cavity teach us KEK K. Hosoyama

2. Electron Positron Collider KEKB Collision Point Tsukuba Nikko Oho Fuji 8 SC-Cavities KEKB LER 3.5 GeV HER 8.0 GeV RF freq. 508.9 MHz Cross. Ang. 2 x 11 m rad. ~ 1km Mt. Tsukuba Photon Factory 2 Crab Cavities Helium Ref. Nikko Tsukuba Need High Luminosity! Global Crab Crossing

3. KEKB Crab Crossing The crab crossing scheme allows a large crossing angle collision without introducing any synchrotron-betatron coupling resonances. 1, 2) 1)R.B.Palmer, SLAC-PUB-4707,1988 2)K.Oide and K.Yokoya, SLAC-PUB-4832,1989 non-crab crossing Original Local Crab Crossing Scheme 4 Crab cavities Global Crab Crossing Scheme 2 Crab cavities Beam-bunch wiggle around the whole ring! Advantage: We can use existing cryogenic system for Acc. S.C. cavities Effect of Crab Crossing (Simulation by Ohmi) Motivation! Local Crab Crossing

4. History of Crab/deflecting Cavity RF Separator KfK, CERN R.B.Palmer K.Oide and K.Yokoya, K. Akai at Cornell for CESR-B Crab Cavity R&D Operation 1991-1992 1989 1977 1994 20072010 2004 Construction 1988 Start of New Era for Deflection Cavities

5. History of KEKB Crab Cavity 1)Full Scale Prototype Crab Cavity 500MHz1996 2 Nb Cavities # 1 & # 2 Coaxial Coupler Prototype Horizontal Cryostat2003 2)KEKB Crab Cavity 509MHz Installation of 2 crab cavities in KEKB was decided 2004 2 Nb Cavities for LER, HER Cold Tested in Vertical Cryostat 2005 Assembling and High power test 2006 Installation and Commissioning 2007 Jan. ~2010 0) 1/3 scale model 1.5 GHz 1994 3 Nb Cavities Fabrication & surface treatment of non-axial symmetric cavity 10 years 3 years Beam Operation > 3 years

6. Characteristic of KEKB Crab Cavity Magnetic Field of TM110 in Squashed Cell Shape cavity High Beam Current HOM / LOM Damped Cavity Large Beam Pipes for Higher Order Coaxial Coupler for TM010 Multipactoring High Power Input Coupler High Power RF Absorber RF Issues Fabrication related Issues Large Dimension (500MHz) Non-axial Symmetric Mechanically Weak Structure Electron Beam Welding Electro-Polishing Cryostat Design Horizontal Coupling Overcomes by RF Processing

7. Conceptual Design of KEKB Crab Cavity The squashed cell shape cavity scheme was studied by Akai extensively at Cornell in 1991 and 1992 for CESR-B under KEK-Cornell Univ. collaboration. We adopted this design as “base design”! Crab Kick TM110 B-field Coaxial Coupler TM010, TE111 Squashed Cell Shape Cavity TM110* Top View Squashed Cell Shape Cavity Design Characteristics: Squashed Cell Shape Higher Order / the Lowest Mode Damped Cavity Coaxial Coupler to Extract TM010 Large Beam Pipes for Higher Order

8. Why we need “Squashed Cell Cavity” TM110TM010 TM110 TE111 500MHz 324MHz 720MHz Unwanted Mode TM110 - like Mode 500MHz TM010 - like Mode 413.3MHz 700MHz 650.5 MHz / 677.6MHz Unwanted Mode Crab Mode E B The squashed cell shape cavity scheme was studied extensively at Cornell in 1991 and 1992 for CESR-B under KEK-Cornell collaboration.

9. KEKB Superconducting Crab Cavity Non-axial Symmetric Structure Thickness of 4.5 mm Nb Cavity Reinforced by Ribs Rib Frequency 501.7 MHz R / Q 46.7  G 220 Esp / Vkick14.4 MV / m / MV Hsp / Vkick415 Oe / MV Mechanical and Fabrication Issues  Max = 17.6 kgf / mm 2  Max = 7.41 kgf / mm 2 No Rib4 - Rib

10. Fabrication of KEKB Crab Cavity Forming of Half-Cells Barrel Polishing 312Hr Electro Polishing Annealing Assembling High Pressure Water Rinsing

11. Effect of High Pressure Water Rinsing 1/3 Scale Model 1.5 GHz Recover By HPR Degraded by Contamination X-Ray Design Value Performance of the cavity degraded by introduce air into cavity by vacuum break and X-ray emission increased. By the HPR, the performance the cavity recovered !

12. Cold Test Stand for KEKB Crab Cavity The crab cavity is taken out from clean room to install into the vertical cryostat. The crab cavity is set in the vertical cryostat Vertical cryostat Clean room Liq. He Dewar 12,000 L He Refrigerator for KEKB superconducting Acc. cavities

13. Multipacting in Crab Cavity with Coaxial Coupler Reflected Power Emitted Power Transmitted Power RF Power On 10:43 11:15 11:25 11:45 Overcome by RF Processing !

14. Multipacting in Crab Cavity with Coaxial Coupler RF test in vertical cryostat (b = 2 ~ 3 ) No multipacting in the crab cavity without a coaxial coupler Multipacting with a coaxial coupler after the 1 st cool down Multipacting could be overcome by about 1 hours RF processing Effect of the RF processing keeps if the cavity keeps at low temperature But, RF high power test in horizontal cryostat (b = 1000 ~ 2000) Could not notice the multipacting Processed by high RF power very quickly! Overcome by RF Processing easily !

15. with coaxial coupler Test Result of KEKB Crab Cavity Prototype #1 without coaxial coupler 4.2 K without coaxial coupler 2.8 K Design Esp Esp [MV/m] Q0Q0 Fabrication and Surface Treatment RF Performance Test with a Coaxial Coupler Multipacting could be overcome by RF process. Crab Cavity #2 Same Performance! Multipacting appeared at very low field but we could overcome by RF processing !

16. Test Result of KEKB Crab Cavity for LER Nov. 18 1 st Test Nov. 29 2 nd Test H.P.R. Field Emission X-Ray EP2 Jan. 13 Test Recovered ! Re-processing Test result could not satisfy the design value! Back to EP II processing.

17. Inspection in the cavity A Whisker Like Foreign Material was found at the heating spot ! Input Coupler Port Small Beam Pipe Trace of Rib 1mm Lint of Cotton Wiper?

18. Design and Fabrication of KEKB Crab Cavity Cryostat No example for designing and construction of Crab Cavity Design Requirement Easy to assemble and disassemble under clean condition Accurate positioning of the coaxial coupler Compact and light weight for installation & transportation in limited space Leak tight for long period operation Stress free at In seal Complex structure and challenging design A prototype cryostat was designed, constructed and cold tested at KEK. R&D efforts for important components Bellows, End cell, Input coupler, HOM damper

19. Conceptual Design of Cryostat for KEKB Crab Cavity Top View Input coupler Magnetic Shield （ Jacket Type ） 80 K LN2 Radiation Shield Coaxial Coupler Stub Support Bellows Main He Vessel Monitor Port RF Absorber Frequency Tuning by Adjusting Distance Crab Mode Reject Notch Filter RF Absorber I.D. 240 I.D.100 Jacket-type Helium Vessel Coaxial Coupler Frequency Tuning Stub-Support -- Mechanical Support & Cooling of Coaxial Coupler Jacket-type Helium Vessel Sub Liq. He Vesse ~ 18 kW at LER 1.6 A 1300 bunch ~ 8 kW

20. Cryostat for KEKB Crab Cavity Input Coupler Beam RF Damper Gate Valve 5 m Weight ~5ton

21. Crab Cavity & Coaxial Coupler in Cryo-module Support Rod for Cavity Invar Jacket Type Main He vessel SUS316L Jacket Type Sub He vessel Coaxial Coupler (Nb) Stub Support Crab Cavity Cell Notch Filter Tuning Pipe and Rod RF Absorber Extract TM 010, TE 111 Mode Frequency Tuning Input Coupler Bellows 1)Crab Cavity is hanged by 4 invar support rods. 2)Coaxial coupler is hanged by 4 stainless rods which are supported by 2 support arms. 3)Head position of the coaxial coupler is controlled by 2 tuning rods. 4)Head of coaxial coupler is cooled by liq. helium supplied from stub support. Support Rod for Stub Support Support Arm

22. Jacket Type Helium Vessel Prototype Jacket Type Magnetic Shield Permalloy 3t Jacket Type Helium Vessel Large Beam Pipe Input Coupler Port

23. Frequency Tuning Mechanism Main Tuner Mechanical + Piezo 6 mm + 200  m Main Tuner : Frequency Tuning ~30 kHz / mm Sub Tuner : Adjust Position of Coaxial Coupler Load Cells Main Liq. He Vessel Input Coupler Stub Support RF Monitor Coaxial Coupler Beam Bellows Driving Plate Cryostat Vacuum End Cell Sub Liq. He Vessel Pick up Probe Driving Rod Sub Tuner Mechanical Support Pipe Top View

24. Frequency Tuner Frequency Tuner Crab Cavity for HER Resonance Frequency Resonance frequency can be controlled by main tuner. Coaxial coupler position can be controlled by sub-tuner. RF Power 6 mm 1 mm 10 dB

25. Main He Vessel Sub He Vessel Input Coupler Stub Support Coaxial Coupler Beam Cooling Water Liq. He In Gas He Cooling System for KEKB Crab Cavity RF Monitor Gas He Bellows RF Absorber RF Absorber Cooling Water Notch Filter Flow Meter Control Valve Cooling Water

26. Assembling Coaxial Structure to Crab Cavity Coaxial coupler was ready to install High Pressure Rinsing Tuning Structure Inner conductor of the assembled coaxial coupler was high pressure rinsed. Head part of the coaxial coupler was installed in to the cavity and assembled. Coaxial coupler was hanged by 4 rods which were connected to 2 support arms.

27. Test Stand for Crab Cavity at D10 Station Sub-transfer Line Control System for RF Test Crab Cavity Acc. Cavity May 12 – June 16, 2006 1 st Test Oct. 24 – Nov. 17, 2006 2 nd Test HER LER Dec. 13 – Dec. 28, 2006 Improved the Problems High Power RF Station Cryogenic System

28. LER HER Q 0 -Measurement Design During high power test at test stand Q 0 were measured by calorimetric method.

29. Installation & Commissioning of Crab Cavities Installation of Crab Cavities for HER Jan. 8, 2007, for LER Jan. 11, 2007 Crab Cavity for HER Crab Cavity for LER Carrying the crab cavity using crane track Cool-down of Crab Cavities Jan. 29, 2007 Beam Operation Start Feb. 13 e-e- e+e+

30. Operation of KEKB Crab Cavities LER HER Beam Current [A] 1.7 1.25 Crab Voltage op. [MV]0.8 - 1.01.3 - 1.6 Crab Voltage max [MV] 1.1 - 1.5 1.7 - 1.8 HOM Power [kW] beam pipe 12.4 6.9 coaxial coupler 2.5 3.0 RF Trips [count / day] 0.5 1.3 Achieved Performances

31. HOM Power of KEKB Crab Cavities HER Crab Cavity LER Crab Cavity Beam Current [ mA ] Beam Pipe Coaxial Coupler 1.7 A 1.25 A 12.4 kW 6.9 kW 2.5 kW 3.0 kW

32. The 15th KEKB Accelerator Review Committee Y. Yamamoto

33. Operation of KEKB Crab cavity The crab cavities operate about 3 years without serious problems. Peak Luminosity L peak =19.6 x 10 33 /cm 2 /s attained under crab on operation. Beam Current Peak Luminosity

34. SUMMARY R&D efforts of 1.5 GHz and 500MHz crab cavities: We have constructed facilities for assembling of the cavities & cold RF test. 2 KEKB crab cavities have been designed, constructed and installed in KEKB, and operate about 3 years under high current beam. KEKB crab cavities shows the potential of superconducting crab cavity for further applications. New era for “application of superconducting crab cavity” is starting! R&D of the KEKB crab cavity tell us; “keep continue” is the “strength”