HOM damper for CRAB Cavity
Yoshiyuki Morita
CRAB cavity
KEKBHOM damper
•••
•

•

Damp HOM (>600 MHz) and LOM (400 MHz)
Ferrite damper
Developed for KEKB superconducting accelerating cavity
HIP (Hot Isostatic Press) : 1500 atm, 900 oC
Size: 240 φ x 120 mm, 4t
Almost the same size of SBP damper used for accelerating cavity
Expected RF load at 1.6 A, 1500-bunch
LBP: 15 kW
Coaxial: 4 kW
Need 4 dampers and 2 spares
9 dampers HIPped, 6 dampers fabricatedFabrication of HOM dampers•••••••••

Baking of ferrite powder
Canning of ferrite powder
HIP 1500 atm, 900 oC
Machining of ferrite surface
UTBaking
Cutting of iron base
EBW of stainless steel flange
Winding of copper pipe•••

High power test: up to 10 kW
Low power test: mode damping test
Evacuation

Before Baking

T. Tajima

Before high power test

UT
#1

#2

#3

#4

#5

#6
#6 has a white circle image
Suggesting bad contact to copper base

UT
#7

#8
#8 has a black dot image
Suggesting a void

#9Baking stand

Baking chamber
HOM damper

O-ringHeaterTemperature vs. pressure2 x 10-5 Pa
Out gassing rate: 6 x 10-10 torr L/s cm2

High power test standRadiation
Thermometer

HOM damper
RF powerDummy
LoadCooling Water

High Power Test
Absorbed Power

Absorbed Power (kW)

16
14
#1
#2
#3
#4
#5
#71210864
200

510 15 20 25 30 35 40 45 50
Input Power (kW)Up to 10 kW
Evaluated by cooling water temperature rise

High Power Test
Ferrite temperature

140oFerrite Temperature ( C)

160
#1
#2
#3
#4
#5
#71201008060
402000510 15 20 25 30 35 40 45 50
Input Power (kW)Measured by radiation thermometerCycle test
50Pin (kW)40High power test

Cycle test
0 – 10 kW, 20 cycles
6 min. interval

Reproducibility check
Power meter calibration

30
20Miss-operation
Pulsed RF power(300 kW, 5 sec.)run through damper

10
0
11:00

12:00

13:00

14:00

15:00

16:00

17:00

18:00

Time
#4 damper experienced 300 kW
Heard cracking sounds
This is the first evidence that the damper has cracks by RF powerLow Power Test
Transmission property

S21 was measured from 400 MHz to2000 MHz.
S21 was calculated using HFSS for
several thickness of the ferrite(nominal thickness: 4 mm).
Simulation with the thickness of 3.5t
agrees with measured data.

Transmission property
0-1

S21 (dB)-2

measured
4t

-3

3.5t
3t-4-5-60

500

1000

1500

Frequency (MHz)

2000

2500

S21 calculation using HFSS

Model Cavity (Cu)
NetworkAnalyzer

Low Power Test
Mode damping

HOM Damper
Coaxial Coupler (Al)Check damping of LOM/HOM
Check validity of simulation

Setup with dummydamper (Al)Mode damping of the model cavity
Mode damping of the model cavity-60

TM510TM410

TE111

TE011

TM310

TE 5/4 λCrab ModeTE 7/4 λTEM 9/4 λTEM 7/4 λTE 1/4λS21 (dB)-40

TE 3/4 λ

LOM
TM110

TEM 5/4 λ

-20

TEM

0without damper
with damper

-80

-100

-120
300

400

500

600

700

800

900

1000

1100

1200

Frequency (MHz)Transmission property of the model cavity with/without the HOM damper. The
LOM and HOMs are sufficiently damped. Q factor of the TE111 is still high,because of its weak coupling to the coupler.

Comparison with simulation
Frequencies and Q factors of several modes.
HFSS simulation agrees with measured data.
HFSS

Measuredmodef (MHz)Qf (MHz)

Q

TM110

402

53

400

47

Crab513

211

515

227

TM310

680

52684

70

TM410

830

162

839

165

TE111

863

1546

871

1424

TM510

993

82

1000

49

Evacuation

Crack mapping

90
Ferrite, 4t x 240 mm dia.

Free flange side

Fixed flange sideθ (deg.)A map of cracks was made after cracking using a micro-scope#4 damper was high power tested and cycle tested again
Cracks were inspected once again
No significant growth of cracks was found

0180

120

Cracks before and after the cycle testCrack Mapping(#4)

Picture No.
9Z (mm)120
110
1009080

101112345670Z (mm)x: Before cycle test
o: After cycle test(10 kW, 20 cycles)

870
60
5040
30
20
100090180
θ (deg.)270360Pictures taken before/after the cycle test
Before

After

1

2

Pictures taken before/after the cycle test
These pictures show no growth of cracking

34

Expected RF power load of LBP damper
3000
5kW

# of bunch

2500

10kW 15kW

20kW

1.5

2.5

2000
1500
1000
500
000.5

1Current (A)23Summary••••••

4 dampers and 2 spares have been fabricated and tested
High Power Test
10 kW absorbed (1500-bunch, 1.3 A)
Cycle test (0 – 10 kW, 20 cycles)
No damageLow Power Test
Transmission property test
Agreed with simulation
Mode damping test using a model cavity
Sufficient damping achieved
Evacuation#1, #2,#3: 5 x 10-11 torr l/sec cm2#1,#2: Assembled#4 : Cracks
Still can be usedHigh power test >10 kW