Crab Cavity Group

Crab Cavity
Crab Cavity R&D GroupK. Hosoyama, K. Hara, A. Kabe, Y. Kojima, Y. Morita,H. Nakai

KEKB and Superconducting Crab Cavity
Characteristics of KEKB Crab Cavity
Fabrication and Surface Treatment of Crab Cavity
RF Performance Test
Horizontal Cryostat for KEKB Crab Cavity
Jacket-type Liquid Helium Vessel
Frequency Tuning
R&D Efforts Nb-Cu Spattering / Cu Bellows

KEKB Crab Crossing
The crab crossing scheme allows a large crossing angle collision
without introducing any synchrotron-betatron coupling resonances. 1, 2)
1)
2)

R.B.Palmer, SLAC-PUB-4707,1988
K.Oide and K.Yokoya, SLAC-PUB-4832,1989

RF Deflector( Crab Cavity )HERElectrons

LER

Positrons

1.44 MV
Head-onCollision

1.41 MV

Required kick 1.44 MV

non-crab crossing

Crossing Angle(11 x 2 m rad.)1.41 MV

1.44 MV

Characteristic of KEKB Crab Cavity
RF Issues
Higher Operation Field Esp = 21 MV/m
Squashed Cell Shape Cavity operating at TM110
Higher Order / the Lowest Order Mode Damped Cavity
Large Beam Pipes for Higher Order
Coaxial Coupler for TM010
Multipactoring
Mechanical Issues
Non-axial Symmetric Weak Structure
Thickness of 4.5 mm Nb Cavity
Reinforced by Ribs

Conceptual Design of KEKB Crab Cavity
Coaxial Input
Coupler

B
Crab Mode
Rejection Filter

EB

Beam

Coaxial Coupler

RF Absorberf > 1.3 GHz
for Monopole Modef > 1 GHz
for Dipole Mode

RF Absorber
TM010 Q < 70
TE111 Q < 20

E
Stub Support

B

Coaxial Input
Coupler

Squashed Cell Shape Cavity
B

Crab Mode

Rejection Filter
Higher Operation FieldE Esp = 21 MV/m
Squashed Cell Shape Cavity operating at TM110
Beam
Higher Order / the Lowest
Order
Mode Damped Cavity
BCoaxial Coupler
RF Absorber
Large Beam Pipes for Higher Order
RF Absorberf > 1.3 Coaxial
GHzCouplerE for TM010 Mode
TM010 Q < 70for Monopole Mode
Stub Support
TE111 Q < 20f > 1 GHz
Multi-pacteringfor Dipole Mode

B

BeamE
BE

Why squashed cell shape cavity?
TM110

TM010

TM110 - like Mode

TM010 - like Mode

500MHz324MHz500MHz413.3MHzBE
Crab Mode
Crab Mode

TE111

650.5 MHz / 677.6MHz

720MHzUnwanted
Mode

Unwanted
Mode
TM110

500MHz700MHzThe squashed cell shape cavity
scheme was studied extensively atCornell in 1991 and 1992 forCESR-B under KEK-Cornell
collaboration.

Superconducting Crab Cavity
Input Coupler
I.D. 240

I.R. 90

I.D. 120

I.D. 188

Coaxial Coupler

I.R.241.5

866

I.R. 20
I.D. 30
Monitor Port

0100

50150483

scale (cm)Non-axial Symmetric Weak Structure
Thickness of 4.5 mm Nb Cavity
Reinforced by Ribs

Electromagnetic Field in Crab Cavity by MAFIAElectric Field in Crab Cavity

RF parameters for Crab Cavity
Frequency

501.7 MHz

R/Q

46.7 ΩG
E-field maximum

Magnetic Field in Crab Cavity

H-field maximum

220

Esp / Vkick

14.4 MV / m / MV

Hsp / Vkick

Oe / MVFabrication & Processing 1NbHalf Cell

Hydro-forming

Grinding ofWelding PartBarrelPolishingFabrication & Processing 2

Electro-PolishingHigh Pressure Water Rinsing
by 80 bar Ultra-Pure water

Annealing at 7000C for 3 hours

Cold Test Stand for KEKB Crab Cavity
He Refrigerator for KEKB
superconducting Acc. cavities

Liq. He Dewar
12,000 L

Clean room

Vertical cryostat

The crab cavity is
set in the verticalcryostat

The crab cavity is taken out from clean room
to install into the vertical cryostat.

Test Result of KEKB Crab Cavity #1
Design Esp
1010without coaxial coupler 2.8 K
Q0

without coaxial coupler
4.2 K

with coaxial coupler

91081005101520Esp [MV/m]

25303540Multipactoring in Crab Cavity with Coaxial Coupler
Reflected Power

10:43

Reflected Power

11:25
Emitted PowerRF Power On

RF Power On

Transmitted Power

Transmitted Power

Reflected Power

11:45

11:15
Reflected Power
Emitted Power

Transmitted PowerRF Power On

RF Power On
Transmitted Power

Emitted Power

Conceptual Design of Cryostat for KEKB Crab Cavity
Frequency tuning by Coaxial Coupler
28.3 kHz / mm
Stub-Support ---- Mechanical Support & Cooling Coaxial Coupler Tip
Jacket-type Helium Vessel
Top View

Input coupler

RFAbsorber

Bellows

I.D. 240

StubSupport

RFAbsorber

Coaxial Coupler

I.D.100

Monitor Port
Liq. He

Liq. He
80 K LN2 Radiation Shield

Crab Mode
Reject Filter

Cryostatfor KEKB Crab Cavity (Top View)
CRYOSTAT FOR KEKB CRAB CAVITY(TOP VIEW)

RF Input Coupler

LN2 InHe Vessel
SupportLHe InGHe Out

Bellows

Coaxial Line Stub Support
LN2 Out
80 K LN2 Shield

00.5

1scale ( m )1.522.5

Cryostat for KEKB Crab Cavity (Side View)
CRYOSTAT FOR KEKB CRAB CAVITY( SIDE VIEW )Mechanical Support

LHe / GHe In & Out

Crab Cavity

Coaxial Coupler

Input Coupler

Bellows
Coaxial Line Stub Support
He Vessel
80K LN2 Shield

00.5

1scale ( m )

1.5

22.5

Cryostat for KEKB Crab Cavity (Front View)

LN2 InLHe InGHe OutSupport

LN2 Out

Crab Cavity

Input Coupler

LHe Vessel
LN2 80K Shield
Vacuum Vessel

0102030
scale ( cm )4050

R&D Efforts
Coaxial Coupler Nb --> Nb-Cu( Designing and Fabrication is very easy ! )To Establish Nb spattering technique
1.5 GHz Nb-Cu Cavity ---- Fabricated and Cold Tested
Seamless Cu Bellows
For Frequency Tuning --- Thin wall (0.4mm) Cu Bellows(Nb-Cu)Forming of Thin Plate
End Plates for Cryostat
Notch Filter

Nb-Cu spattering Cavity

Temperature 300 ~ 350 0C
Ar Gas
0.2 PaRF Power 100kW 13.56 MHz

1.5 GHz Nb-Cu Cavity

RF coupler

HeaterRadiation shield
Vacuum chamber
Magnet
SUS316L

SUS316L
C1011

Cu cavity
Nb target

Nb-Cu 1.5 GHz Cavity

9Q01081071002468
Esp [MV/m]

101214Nb-Cu Cavity
1.5 GHz Nb-Cu Cavity
Spattering Chamber for Nb-Cu Cavity

Cu Bellows

Stress Analysis by ABAQUS

R = 3 mmt = 0.4 mm

I.D. 188

Allowable Deformation ΔL of Bellows

ΔL allowable (mm)Pitch 17.9 mm

Stress σ (Mpa)t = 0.4 mm, Δ L = 1 mm

Young’s Modulus
E = 127,000 Mpa
Poisson Ratio
ν = 0.34

5000 cycles
for 6-cell Bellows

Thickness of Bellows (mm)Fabrication of Bellows -Seamless PipeThin Wall thickness Cu Pipe I.D. 188 mm t = 0.5mm
Seamless Pine

Cu Diskt = 2mm

FormingMandrel, Die andFabricated Cu-pipe

Drawing
Side wall

Drawing;using smaller diesstep by step
without annealing
Drawing BenchCapacity 30 t

Fabrication of Bellows

Press Unit andPressure Water Pump

Fabricated 5-cell Bellows

Set the Female DieFemale Dieand Outer
Guide Pipe

Clean Room for Cavity and Cryostat Assembling
Clean Room ( Class 100 )for Cavity AssemblingHigh Pressure Pure
Water Rinsing
Clean Room
for Cryostat Assembling

End Plate of Vacuum Vessel for Cryostat
made by Spinning

Installation of Crab Cavity into KEKB Tunnel

Cryostat for Crab Cavity

05Scale (m)Cryogenic System for Crab Cavity
Satellite Refrigeration System for KEKB Crab Cavities
Nikko Experimental Hall

RequiredAmount of Supply

Heat Load of
Crab Cavities (4 units)

Heat Loadof Transfer Line (1km)

Liq. Helium (4.4K)

400 W x 2 = 800 W

1000 m x 0.2 W/m = 200 W 350 L / hr

Liq. Nitrogen (80K)

300 W x 2 = 600 W

1000 m x 5 W/m = 5000 W 129 L / hr

Cryogenic System
for Superconducting
Acc. Cavities
Helium Refrigerator
8 kW at 4.4 K

Liq. Helium
350 L/hr
Liq. Nitrogen 169 L/hr

Liq. Helium Transfer Line1 km
NTsukuba Experimental Hall
Crab Cavities#1 and #2

Crab Cavities#3 and #4

Satellite Ref. 1

Satellite Ref. 2

Cooling Capacity
400 W at 4.4 K

Cooling Capacity
400 W at 4.4 K

Satellite Refrigeration System for Crab Cavities
Satellite Refrigeration System
for KEKB Crab Cavities

TsukubaHelium Compressor Unit
1800 Nm3 / hr

Nikko

Satellite Ref. 1
400 W at 4.4 K
Satellite Ref. 2
400 W at 4.4 K

Gas Helium 12.2 g /s
245 Nm3 / hr

Helium Ref.
8 kW at 4.4 K

Liq. Helium Transfer Line 1 km
Liq. Helium
350 L / hr

Crab Cavity #1

Crab Cavity #3

Crab Cavity #2

Crab Cavity #4

12,000 L
Liq. Helium