1. R&D for Fundamental Power Coupler in SRF Mass-Production
Y. Yamamoto, E. Kako, T. Matsumoto, S. Michizono, H. Sakai, A. Yamamoto (KEK)
C. Arcambal, E. Cenni (IRFU/CEA)
Kirk
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2. FJPPL Workshop 2017 @Strasbourg
Outline
Recent Large-scale SRF Accelerators
Motivation (Goals for this R&D)
R&D Items
Summary
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3. On-going Large-scale SRF Accelerators
In recent years, SRF accelerator with several hundred cavities is standard in the world!
Project
Region
Particle
Beam energy RF
# of cryomodules
# of cavities / cryomodule
# of cavities
# of couplers
E-XFEL EU
Electron
17.5 GeV
1.3 GHz
101 8
808
LCLS-II
U.S.
4 GeV 35
280
ESS
Proton
2 GeV
352 MHz (Spoke)
704 MHz (Med., High) 13 9 21 2 4 26 36 84
Many R&Ds for cavity have been well-done, but as for power coupler, not so… ↓
We’d like to focus on power coupler, especially, for mass-production like ILC.
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4. Goals for Power Coupler R&D
Optimization in preparation/inspection works and RF conditioning method
Rinsing procedure
Ultrapure water rinsing
Ultrasonic rinsing
Ozonized (O3) water rinsing
Inspection tools
What tools we can use
Full or Semi-automation?
RF conditioning method
How many steps for optimization?
Which technical interlock system is used?
Cost reduction
TiN coating-free ceramic
Lower cost design
We’d like to fix the optimum method in each item!
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5. Test Samples for Ceramic & Copper Plating
φ19 x 3 (20 pieces)
100 x 50, 25μm (20 pieces)
We already fabricated some test samples of ceramic and copper plating for the rinsing R&D.
We will check the rinsing effect for various rinsing conditions.
After that, we will try for power coupler similarly, and compare the RF conditioning time.
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6. Test Power Couplers & Test Bench
(TETD)
Product No.
Serial No.
Ceramic company
Ceramic color
Ceramic
coating
Warm #1, #2
E42130
14L001
14L002
NGK/NTK
White
TiN
Cold #1, #2
Cold #3, #4
14L003
14L004
KYOCERA
Gray
free
Ceramic
Ceramic
Warm part
Cold part
The both inner surfaces are copper-plated.
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7. Various rinsing procedures
Ultrasonic rinsing in E-XFEL
Ultrapure water rinsing in STF
O3 water rinsing in Super-KEKB
1st step: To be done for test samples
Surface inspection by microscope
Measurement of secondary electron emission
2nd step: To be done for test power couplers
Comparison of RF conditioning time
Courtesy of Sakai-san in ARES group
Courtesy of W. Kaabi
FJPPL Workshop

8. How to check rinsing effect
Ceramic:
Measurement for secondary electron emission coefficient
Copper plating:
Inspection by microscope
Peeling test by 3M tape
SEE measurement device
C. Arcambal recommended this 3M tape!
Courtesy of Hisamatsu-san
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9. Inspection tools for copper plating
Semi-automatic inspection system for cavity in STF
We already developed the semi-automatic inspection system for cavity,
but still not for power coupler.
That is actually necessary for power coupler?
Or, it is enough for the manual inspection?
Digital borescope (J-SCOPE)
Rigid borescope (OLYMPUS)
Digital borescope (OLYMPUS)
Courtesy of Takenaka-san
FJPPL Workshop
Courtesy of Tanaka-san
Courtesy of Higo-san

10. RF conditioning method
E-XFEL
STF
Vacuum I/L: 1~2 x 10-4 Pa
Arc I/L: Warm part & Waveguide
Electron emission I/L: none
Ceramic temperature I/L: none, but <50℃
How many steps for pulse width is necessary?
Which technical I/L is necessary?
How much is the threshold level?
Courtesy of W. Kaabi
FJPPL Workshop

11. Power Coupler with TiN coating-free ceramic
Unusual vacuum level in higher RF duty ↓
T-mapping attached
Unusual heating in tapered section
High power test was interrupted
Particle simulation was done
Secondary electrons can propagate to tapered section
Ultrasonic rinsing will be done
Material search restarts
New coupler will be fabricated
Made in KYOCERA
LSEEC
Electrical
Property
Volume Resistivity
ohm･cm -
Surface Resistivity
ohm/□
1.2 X 1014
SEE　Coefficient
3.2
Dielectric Constant
1MHz
8GHz
10.0
Dielectric Loss Angle
3 X 10-3
Many secondary electrons emitted from ceramic surface
can propagate up to tapered section!
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PIC solver in CST

12. Enough budget for these R&Ds is expected in F.Y. 2018.
Lower cost design
Cost reduction is urgent issue for ILC!
L. Evans
There are two candidates for power coupler in ILC.
How are they merged?
Which design is lower cost?
Enough budget for these R&Ds is expected in F.Y
FJPPL Workshop

13. FJPPL Workshop 2017 @Strasbourg
Summary
Power coupler R&D for mass-production should be focused
R&D for test samples is already starting
New material for TiN coating-free ceramic is searching
We will discuss the contents for this R&D during IPAC2017 in Copenhagen next week!
FJPPL Workshop