WG D: HOM Couplers and LoadsSummary

G. Burt & J. Delayen

N. Valles – Cornell ERL Main Linac HOM load Research and Development

3

Description of Beamline HOM Load• HOM beamline absorber located between cavities in ERL linac at 40 to 80 K• Based on the first generation ERL HOM load but greatly simplified and improved

• RF absorbing material: SiC produced by Coorstek (SC-35)• Broadband RF loss

– ε = (50 – 25i) ε0

– μ = μ0

• Sufficient DC conductivity at 80 K• No measured particulate generation

– Tested with high pressure nitrogen gas– Can be high pressure rinsed

• Vacuum properties acceptable

N. Valles – Cornell ERL Main Linac HOM load Research and Development

4

Initial SiC Sample Measurements

5.0

5.2

5.4

5.6

5.8

6.0

50 150 250 350Co

nduc

tivity

s[1

/Wm

]Temperature [K]

SiC

• Initial RF Measurements give ε ~ (50 – 25i) ε0

• Discontinuities in measurement could be indications of• Measurement error• Inhomogeneity in material• Effervescent (ghost) modes

• Good DC conductivity at cryogenic temperatures• Key to avoiding charging HOM absorber by

beam or field emission

N. Valles – Cornell ERL Main Linac HOM load Research and Development

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Cryogenic Test of Power Absorption• 125 W (limited by heater) applied to HOM

absorber at cryogenic temperatures to simulate HOM heating

• Thermal cycled without any problems• Thermal properties as expected• ∆T over load very small at 125 W (<10K)

• ∆T shown below is for cooling gas

N. Valles – Cornell ERL Main Linac HOM load Research and Development

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RF Absorber Measurement

Coax transmission measurement setup with prototype beam line loadAttenuation of the forward power is roughly consistent with the estimates for ε = (50 – 25i) ε0

Introduction; Concept of Demountable Damped Cavity (DDC)

26 June 2012 Higher Order Mode Diagnostics & Suppression in SC Cavities: Group D 8

He Vessel Baseplate

HOM

Acc.

Choke Coaxial waveguide RF absorber

Accelerating Mode is reflected by choke filter.HOMs pass through the choke, and damped at the RF absorber

RF simulations

26 June 2012

Higher Order Mode Diagnostics & Suppression in SC Cavities: Group D 9

0

0.2

0.4

0.6

0.8

1

1.2

1.4

0 10 20 30 40 50

Mu

ltip

lica

tio

n F

act

r

Eacc [MV/m]

Accelerating cell

Choke

CST-Studio

-50

0

50

100

150

200

250

300

350

226 228 230 232 234

L [

mm

]

Qcoupling

=776

Qcoupling

=791

Qcoupling

=809

[mm]

n=0

n=1

Resonate frequency of the cavity

n=2

The coupling (Qcoupling) is about 790.

LTop of inner conductor15mm

End of inner conductorCavity iris

-150

-140

-130

-120

-110

-100

-90

-80

-70

1292 1292.02 1292.04 1292.06 1292.08 1292.1

S21

[d

B]

Frequency [MHz]

-90 [dB]

25 kHz

RF Absorber (Ferrite: CMD10)

26 June 2012 Higher Order Mode Diagnostics & Suppression in SC Cavities: Group D 10

0.1

1

10

100

10 100 1000 104

'''

Frequency [MHz]

'

'' HOM region

=12.0

22 )/(1)/(11'

DomainWall

DomainWall

Spin

Spin

20

2

0

)/(1

/

)/(1

/''

DomainWall

DomainWall

Spin

Spin

RF absorber is mounted on 77K thermal anchor. Because brazing is included the manufacturing process, this ferrite was annealed at

900 ℃ before the measurement.

Ferrite

To vacuumpump

Liquid nitrogenInput

Refection

Transmission d

S11

S21

Network 　Analyzer

Coaxial waveguide

RF Absorber(Ferrite)

The permeability and permittivity were estimated by fitting.

Imaginary part is larger than real part in HOM regionWe conclude this ferrite has sufficient absorbing ability at 77K.

107

108

109

1010

1011

0 5 10 15 20

Qo(8th)

Qo(9th)

Qo(10th)

Qo(12th)

Qo(13th)

Qo(16th)

Qo(17th)

Qo(18th)

Qo

Eacc [MV/m]

1.8W

5W

Superconducting joint

26 June 2012 Higher Order Mode Diagnostics & Suppression in SC Cavities: Group D

11

Base plateFlange

ChokeFlange

Indium

Nb

Ti

8th 9th, 10th 12th, 13th 16th, 17th, 18th

10-9

10-8

10-7

10-6

10-5

1.5 2 2.5 3 3.5 4 4.5

Rs [Ω](8th)Rs [Ω](9th)Rs [Ω](10th)Rs [Ω](12th)Rs [Ω](13th)Rs [Ω](16th)Rs [Ω](17th)Rs [Ω](18th)

Rs

[W]

T [K]

Transition temperatureof Indium = 3.4 K

Hit the periphery ahead

Torque:25, 30, 35(N ･m)

No X-ray

t2mm

t2mm

t100mm

The magnetic field at the superconducting joint is 1/6 of the cavity’s maximum field.

Sealing material is indium. Its transition temperature is 3.4K. Step by step, we changed the flange edge shape to achieve higher

performance

Transition temperature was observed at 3.4K in 8th~17thVT.This means indium had been exposed to the RF field.

Finally, we achieved 19MV/m, Qo=1.5×1010

Knife edge

This Q-switch occurred by thermal quench of indium.

To solve this, knife edge structure was introduced.

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HOM coupler options

WG coupler

Coaxial with high pass filter

Coaxial performance

Comparison