1. KEKB Crab Development K. Hosoyama (KEK) Crab Cavity for HER Crab Cavity for LER Crab Cavity for KEKB History of Crab Cavity R&D Characteristics of Crab Cavty Cryostat for Crab Cavity Frequency Tuner High Power Test at D10 Test Stand Commissioning of Crab Cavities for KEKB Summary

2. Crab Cavities for 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. Mt. Tsukuba Photon Factory 2 Crab Cavities Nikko Tsukuba 2 Crab Cavities at “Nikko” Helium Ref. Beam-bunch wiggle around the whole ring! Advantage: We can use existing cryogenic system for Acc. S.C. cavities

3. Milestone of KEKB Crab Cavity Development 1)Full Scale 500MHz Prototype Crab Cavity 2 Nb Cavities # 1 & # 2 Coaxial Coupler Prototype Horizontal Cryostat ( # 2 was Installed into Prototype Horizontal Cryostat for Cool down Test) Installation of 2 crab cavities in KEKB was decided 2) KEKB Crab Cavity 509MHz 2 Nb Cavities for LER, HER Cold Tested in Vertical Cryostat Assembling and High power test Installation Commissioning and Operation 0) 1/3 scale 1.5 GHz model 1994 1996 2003 2005 2006 2007 ~ 2010 2004

4. Conceptual Design of KEKB Crab Cavity E EB The squashed cell shape cavity scheme was studied extensively by Akai at Cornell in 1991 and 1992 for CESR-B under KEK-Cornell 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

5. Characteristics of KEKB Crab Cavity “Squashed cell shape” design is adopted to push up the unwanted regenerative mode of the TM 110 crab mode up 700MHz Higher Order / the Lowest Mode Damped Cavity; Large beam pipe is designed for Higher Order Mode damping Coaxial coupler is put into the cell through beam pipe for the Lowest TM 010 acceleration mode damping Coaxial coupler must adjust on axis of crab cavity Head of coaxial coupler must cool to keep superconductive state Notch filter in the coaxial coupler reject outgoing crab mode Big concern for the Multipacting at coaxial coupler Non-axial symmetric and large in size cavity design Need care in designing, fabrication and EP of the cavity

6. Why squashed cell shape cavity? TM110TM010 TE111 500MHz 324MHz 720MHz TM110 - like Mode 500MHz TM010 - like Mode 413.3MHz 700MHz 650.5 MHz / 677.6MHz Unwanted Modes 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. Degenerative Mode TM110 Unwanted Modes

7. KEKB Superconducting Crab Cavity Non-axial Symmetric Structure Thickness of 4.5 mm Nb Cavity Reinforced by Ribs Simplified Coaxial Coupler

8. with coaxial coupler Test Result of Prototype #1 Crab Cavity without coaxial coupler 4.2 K without coaxial coupler 2.8 K Design Esp Esp [MV/m] Q0Q0 RF Performance Test with a Coaxial Coupler; Multipacting was observed at very low RF power, but we could overcome by RF process.

9. 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 Filter RF Absorber I.D. 240 I.D.100 Frequency Tuning Coaxial Coupler ~30 kHz / mm Stub-Support -- Mechanical Support & Cooling of Coaxial Coupler Jacket-type Helium Vessel (Main He Vessel and Sub He Vessel ) Jacket-type Magnetic Shield Sub Liq. He Vesse ~ 18 kW at LER 1.6 A 1300 bunch ~ 8 kW Characteristics

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

11. 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

12. Main Liq. He Vessel Input Coupler Stub Support RF Monitor Coaxial Coupler Beam KEKB Crab Cavity Frequency Tuner Main Tuner Mechanical + Piezo 6 mm + 200 mm Bellows Driving Plate Cryostat Vacuum End Cell Sub Liq. He Vessel Pickup Probe Main Tuner : Frequency Tuning ~30 kHz / mm Sub Tuner : Adjust Position of Coaxial Coupler Tuning Rod Sub Tuner Mechanical Support Pipe Load Cells Top View 1)The jacketed crab cavity is fixed to the vacuum vessel. 2)Insertion of the coaxial coupler to the crab cavity is controlled by changing position of the sub liquid helium against the end plate by two driving rods. 3) Transverse position of coaxial coupler tip is controlled by adjusting distance D R and D L. DRDR DLDL If the coaxial coupler set in center of crab cavity, there is no RF power flow to pickup probe.

13. Frequency Tuner Test 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 Dip of RF power means good position! RF Power at Pickup Probe

14. Insertion of Coaxial Coupler (1/2) Slide Rotate Assembling the coaxial coupler to the cryostat was very “tough job” Inner conductor of coaxial coupler must be connect tightly without gap. ------ Bayonet type connection was adopted Precise alignment was needed; not only the position of axis but also direction of axis ! The insertion tool must be rigid enough to support heavy component and need precise adjustment knobs.

15. Insertion of Coaxial Coupler (2/2) Crab Cavity (Cryostat) SideNotch Filter Side We could assemble it by using improved Insertion tool!

16. Move to Test Stand for Cool-down & High Power Test Mt. Tsukuba Crab cavity for HER April 26, 2006 1st Oct. 16, 2006 2nd Crab cavity for LER Dec. 6, 2006

17. Final High Power Test at Test Stand Crab cavity for HER and LER were cooled down without leakage. Resonant frequency could adjust to operating frequency of 508.9MHz. V kick = 1.8 MV and 1.93 MV respectively, exceed the design value of 1.44 MV. Qo – values at design kick voltage were higher than 1x10 9. Cavity and coaxial coupler was cooled stably during the high power test. Cryogenic system worked very well! Frequency tuner of crab cavity HER work very well and Phase stability of crab cavity HER is good. Phase stability of crab cavity LER is not good, but this problem could be saved by RF feed-back system.

18. 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+

19. SUMMARY During more than 10 years of crab cavity development, We designed and fabricated the crab cavities and related components including the cryostat. We construct the facilities for assembling and cold RF test. 2 KEKB crab cavities have been constructed and installed in KEKB. The crab cavities operate more than 3 years without serious problems. The peak luminocity L peak = 20 x 10 33 /cm 2 /s was attained under crab on operation. By the successful construction and operation of KEKB crab cavity, the reliability of superconducting crab cavity was proved for future application.