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.