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KEKB Crab DevelopmentK. Hosoyama (KEK)
Crab Cavity Group
Crab Cavity for HER
Crab Cavity for LER
Crab Cavity for KEKBHistory of Crab Cavity R&DCharacteristics of Crab CavtyCryostat for Crab CavityFrequency TunerHigh Power Test at D10 Test StandCommissioning of Crab Cavities for KEKBSummary
Crab Cavities for KEKB
Collision Point
Tsukuba
Nikko
Oho
Fuji
8 SC-Cavities
KEKBLER 3.5 GeVHER 8.0 GeV RF freq. 508.9 MHzCross. Ang. 2 x 11 m rad.
Mt. Tsukuba
Photon Factory
2 Crab Cavities
NikkoTsukuba
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
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
20052006
2007 ~ 2010
2004
Conceptual Design of KEKB Crab Cavity
E
EB
TM010 Q < 70TE111 Q < 20
RF Absorber
Beam
Stub Support
Crab ModeRejection Filter
RF Absorber
Coaxial InputCoupler
f > 1.3 GHz for Monopole Modef > 1 GHz for Dipole Mode
E
Coaxial Coupler
B
B
B
E
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-fieldCoaxial Coupler TM010, TE111Squashed Cell Shape Cavity TM110* Top View
Beam
E
EB
E : Electric FieldB : Magnetic Field
Squashed Cell Shape Cavity
Characteristics of KEKB Crab Cavity
• “Squashed cell shape” design is adopted to push up the unwanted regenerative mode of the TM110 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 TM010 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
Why squashed cell shape cavity?
TM110 TM010
TE111
500MHz
500MHz
324MHz
720MHz
TM110 - like Mode
500MHz
TM010 - like Mode
413.3MHz
700MHz
650.5 MHz / 677.6MHz
Unwanted Modes
Crab ModeCrab 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
KEKB Superconducting Crab Cavity
I.R. 20
I.R. 90
I.D. 188
I.D. 120
I.D. 30
I.D. 240
Input Coupler
Monitor Port
I.R.241.5
483
866Coaxial Coupler
scale (cm)
0 50 100 150
Non-axial Symmetric Structure Thickness of 4.5 mm Nb Cavity Reinforced by Ribs
Simplified Coaxial Coupler
108
109
1010
0 5 10 15 20 25 30 35 40
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]
Q0
RF Performance Test with a Coaxial Coupler;Multipacting was observed at very low RF power, but we could overcome by RF process.
Conceptual Design of Cryostat for KEKB Crab Cavity
Top ViewInput coupler
Magnetic Shield ( Jacket Type )
80 K LN2 Radiation Shield
Coaxial Coupler
Stub Support
BellowsMain He Vessel
Monitor Port
RF Absorber
Frequency Tuningby 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
atLER 1.6 A 1300 bunch
~ 8 kW
Characteristics
Cryostat for KEKB Crab CavityInput Coupler
Beam
RF Damper
RF Damper
Gate Valve
5 m Total Weight ~5ton
Crab Cavity & Coaxial Coupler in Cryo-module
Support Rod for Cavity InvarJacket 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 TM010, TE111 ModeFrequency 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
Main Liq. He VesselInput Coupler
Stub SupportRF Monitor
Coaxial Coupler
Beam
KEKB Crab Cavity Frequency Tuner
Main TunerMechanical + Piezo 6 mm + 200 mm
Bellows
Driving Plate
Cryostat Vacuum End Cell
Sub Liq. He Vessel
Pickup Probe
Main Tuner : Frequency Tuning ~30 kHz / mmSub Tuner : Adjust Position of Coaxial Coupler
Tuning Rod
Sub TunerMechanical
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 DR and DL.
DR
DL
If the coaxial coupler set in center of crab cavity, there is no RF power flow to pickup probe.
Frequency Tuner Test
Frequency Tuner Crab Cavity for HER
Res
onan
ce F
requ
ency
• Resonance frequency can be controlled by main tuner.• Coaxial coupler position can be controlled by sub-tuner.
RF
Pow
er
6 mm
1 mm
10 dB
Dip of RF power means good position!
RF Power at Pickup Probe
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.
Insertion of Coaxial Coupler (2/2)
Crab Cavity (Cryostat) Side Notch Filter Side
We could assemble it by using improved Insertion tool!
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
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.
• Vkick = 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 1x109.
• 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.
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 , 2007Beam Operation Start Feb. 13
e-
e+
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 Lpeak = 20 x 1033 /cm2/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.