Advance on High Power Couplers for SC Accelerators

Eiji KAKO (KEK, Japan) IAS at Hong Kong, 2017 Jan. 23 1

Advance on High Power Couplers for SC Accelerators

Eiji Kako (KEK, Japan)

IAS conference at Hong Kong for High Energy Physics, 2017, January 23th

Introduction of high power couplers

Essential technical issues on couplers

High power couplers for CEPC

Summary

OUTLINE






Summary

OUTLINE


Essential Consideration for Input Couplers

RF power capability : ( PRF = Ibeam * Vacc * cosφ ) Coupler type : coaxial or waveguide Ceramics window type : disk or cylindrical Number of windows : single or double Coupling with cavity : fixed or adjustable Cooling method : air, He-gas, N2-gas or water Bias voltage : useful or needless

1. Input coupler is one of the most critical component of an SRF system. 2. Design of an input coupler strongly depends on a cryomodule structure.


Important Technical Issues for Input Couplers

Ceramics window : material, purity Metalizing of ceramics Copper plating : thickness, RRR, adhesion, pits, uniformity TiN coating : thickness, uniformity Joining by Brazing Welding by TIG, Laser, E-beam

RF properties Thermal characteristics Mechanical analysis Multipacting simulation

Cleaning procedure Assembly in clean room


From coupler design to beam operation

Design/Calculation Fabrication RF measurement

Cleaning/Assembly Pumping/Baking

Cavity string assembly in clean room

Conditioning at RT in cryomodule

High power test at LT and, then

operation with beam Conditioning at

test stand


- Design: maximum power per coupler, multi-coupler per cavity. - Construction: choice of material and techniques of construction, coating method. - Series production: fabrication, cleaning, handling and assembly. - Series production by industrials: modification of the processes, industrial alternative proposals, ... - Cleaning and assembly: which clean room is really needed, for FPC alone, for FPC onto cavity. - Tests: prototype processes versus series processes, RF test boxes, amplifiers for tests. - Statistics: couplers operated in accelerators. - Diagnostics: during R&D and prototyping, diagnostics during operation in accelerators. - Degradation: characteristic over time of beam operation

Discussion topics for high power couplers


TRISTAN-type High Power Input Couplers

Original design : 508 MHz TRISTAN Input Coupler S. Noguchi, E. Kako, K. Kubo (4th SRF-WS, 1989 )

508 MHz KEKB Input Coupler (KEK)

704 MHz HIPPI Input Coupler (CEA)

805 MHz SNS Input Coupler (ORNL)

972 MHz ADS Input Coupler (KEK)

1300 MHz cERL Injector Input Coupler (KEK)


High Power Performance of TRISTAN-type Couplers

Facility Frequency Window type Coupling

Maximum RF Power

TRISTAN /KEK 508 MHz Coax. Disk Fixed

Test-stand, 200 kW, CW Operation, 70 kW, CW

KEKB /KEK 508 MHz Coax. Disk Fixed


HIPPI /CEA 704 MHz Coax. Disk Fixed

Test-stand, 1.2 MW, pulse (10% duty)

SNS /ORNL 805 MHz Coax. Disk Fixed

Test-stand, 2 MW, pulse Operation, 350 kW, pulse

ADS /KEK-JAERI 972 MHz Coax. Disk Fixed

Test-stand, 2 MW, pulse Operation, 350 kW, pulse

cERL-Inj. /KEK 1300 MHz Coax. Disk Fixed


All of these RF windows were fabricated by Toshiba-ED company.





Summary

OUTLINE


About 30 years ago in TRISTAN at KEK

508MHz, CW 50kW Input coupler with one warm window and water cooling

In the initial stage, no TiN coating no Arc sensor

Importance of TiN coating and Interlock system

(at test stand, 1988’)


Outer conductor

Inner conductor

RF conditioning at test stand for 1.3 GHz CW input couplers

Excessive heat-up Cu-bellows

Cu-tube

after 100 kW CW conditioning


1.3 GHz CW Input Couplers for cERL Injector Cryomodule

Droplet of water on ceramic during cool-down


Quality control of Cu-plating : projection

Test piece with micro-projections

Test piece with smooth surface

Micro-projection (φ100µm) were formed after brazing at 800oC. The cause was organic carbon contamination in an old solution.


RF window troubles in recent coupler development


Cu-plating troubles in recent coupler developments





Summary

OUTLINE


CEPC SRF hardware specification Hardware Qualification Normal Operation Max. Operation

650 MHz 2-cell Cavity VT 4E10 @ 22 MV/m HT 2E10 @ 20 MV/m 2E10 @ 16 MV/m 2E10 @ 20 MV/m

1.3 GHz 9-cell Cavity VT 3E10 @ 25 MV/m 2E10 @ 20 MV/m 2E10 @ 23 MV/m

650 MHz Input Coupler HPT 300 kW sw < 254 kW 280 kW

1.3 GHz Input Coupler HPT 20 kW peak, 4 kW avr. < 15 kW peak 18 kW peak

650 MHz HOM Coupler HPT 1 kW < 0.2 kW 1 kW

650 MHz HOM Absorber HPT 5 kW < 2 kW 5 kW

650 MHz Cryomodule (six 2-cell cavities) static loss 5 W @ 2 K static loss 8 W @ 2 K static loss 10 W @ 2 K

Tuner (MR & Booster) tuning range / resolution 400kHz/1Hz 200 kHz / 1 Hz 400 kHz / 1 Hz

LLRF (MR & Booster) amp & phase stability 0.1%, 0.1 deg

amp & phase stability 1%, 1 deg

amp & phase stability 0.1%, 0.1 deg

by J. Zhai (IHEP)


650 MHz 2-cell cavity for CEPC

Parameters Value

Riris (mm) 78 Alpha (deg) 3.22 A (mm) 94.4 B (mm) 94.4 a (mm) 20.123 b (mm) 22.09 L (mm) 115.3 D (mm) 204.95 k 2.86% R/Q (Ω) 213 G (Ω) 284 Ep/Eacc 2.4 Bp/Eacc [mT/(MV/m)] 4.2

kloss (total) [V/pC] 0.81 (bunch length 4 mm)

Cut-off frequency of beam tube (MHz)

TE11：1126 TM01：1471

by J. Zhai (IHEP)


CEPC 650 MHz Cryomodule

by J. Zhai (IHEP)


Recent new development of high power couplers cERL Injector Cryomodule

(KEK) bERLinPro Booster Cryomodule

(HZB) by A. Neumann (HZB)

by E. Kako (KEK)

1.3 GHz, CW 100 kW Coupler 1.3 GHz, CW 120 kW Coupler

Under beam operation Under construction


Machine Parameters CEPC CEPC Beam Energy 120 GeV 6 -> 120 GeV Beam Current 16.9 mA 0.9 mA Circumference 55 km 55 km

Total RF Voltage 3.5 GV 0.2 -> 5.2 GV Coupler Parameters Collider Ring Booster Ring

RF Frequency 650 MHz 1300 MHz Accelerating Gradient 16 MV/m 20 MV/m Cavity Effective Length 0.46 m (2-cell) 1.04 m (9-cell)

Required RF Power CW, 210 kW Peak, 20 kW

Coupler specification of SC cavities for CEPC


CEPC high power coupler

650 MHz coupler 300 kW CW, assemble with cavity in class 10 cleanroom, inner conductor water cooling, outer conductor He gas cooling, fixed or variable coupling.

1.3 GHz coupler 20 kW peak, 4 kW average, no cooling, variable coupling.

by J. Zhai (IHEP)


SUMMARY

Development of high power couplers is always challenging work.

Many technical issues to be solved are still existing in highly reliable couplers for a stable beam operation.

RF conditioning of prototype couplers at the test stand for CEPC should be started in an early stage.

KEK will join and cooperate on R&D of high power couplers for CEPC.


Thank you for your attention.

Documents

Advance on High Power Couplers for SC Accelerators