1. T. Saeki (KEK) 15 May 2014 AWLC2014 at FNAL
VEP studies at STF/KEK
T. Saeki (KEK)
15 May 2014
AWLC2014 at FNAL

2. Electro-polishing (EP) process
EP is thought to be the best final surface-polishing process of ILC 9-cell cavity to achieve high-gradient specification of ILC.
EP is also most complicated/costy surface-preparation process in the cavity mass-production of ILC.
The current standard EP method is called “horizontal EP process”, where a cavity is set up in a horizontal posture and the cavity is rotated during the EP process.
In order to achieve simpler and more cost-effective EP process, ”vertical EP process” is studied in many laboratories in the world, where a cavity is set up in a vertical and fixed posture.

3. Horizontal EP (HEP) / Vertical EP (VEP)
Rotation of cavity in HEP process.
(HEP setup at KEK-STF)
EP electrolyte is fully filled.
EP electrolyte is half filled.
Turning the EP-bed for draining
No rotation of cavity in VEP process.
(VEP setup at Saclay)

4. Horizontal EP / Vertical EP
Horizontal EP (HEP)
Asia: KEK-STF
Europe: DESY, Saclay, RI, Zanon
US: FNAL, ANL, Jlab, AES
Vertical EP (VEP)
Asia: KEK / Marui Galvanizing Co. Ltd.
Europe: Saclay
US: Cornell, JLab
I will present these activities.
Vertical electro-polishing (VEP)
・No need of large space
・No need of cavity rotation
・No need of horizontal-vertical
conversion system
More suitable for mass production

5. Development of retractable wing-shape cathode in collaboration with Marui Co. Ltd.
The retractable-wing cathode to realize uniform flow of electrolyte and uniform distribution of electric current.
EP electrolyte is circulated to remove hydrogen gas and for low temperature.
Flow direction
Acid bath
Pump
Side View
Top View
Opened
Retracted Al
Rotation of cathode
Marui Galvanizing Co. Ltd. named the cathode “Ninja”, which is registered as a trade name.

6. VEP experiments with “Ninja” cathode
1, VEP experiments with two single-cell cavities for vertical tests
・To optimize VEP condition and evaluate acceleration gradient
2, VEP experiments with one coupon single-cell cavity
・To investigate the relationship between VEP condition (temperature, current, etc.)
and surface state after VEP (roughness, removal thickness etc.)
・To achieve more uniform VEP
3, VEP experiments with one 9-cell cavity for vertical tests
・To optimize VEP condition and evaluate acceleration gradient
・To develop the VEP mass production system

7. VEP experiment with single-cell cavity
VEP setup
single-cell cavity
VEP condition (an example)
EP solution: H2SO4(98%):HF(55%)=9:1
Voltage: 9V
Flow rate: 5L/min
Cathode rotation speed: 5rpm
EP duration: 90min
Flow direction: Bottom to top
Schematic view of VEP setup

8. Development of retractable wing-shape cathode in collaboration with Marui Co. Ltd.
The hydrogen gas generated during EP process is the most difficult problem.
Lower side: smooth.
Upper side: stripe by bubbles.
Flaws observed after VEP with inadequate parameters (voltage, temp, flow rate, etc...):
Stripe on surface (due to bubbles)
Rough surface
These problems should be overcome.

9. VEP experiment with single-cell cavity
Logged data (Temperature-time)
Logged data
(Voltage, Current density-time) 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24
Upper
Inner surface of cavity
Removal thickness
In the next step, we would like to do vertical test and know
the acceleration gradient of VEP’ed cavity.
Lower

10. Plan of VEP + VT with single-cell cavity in collaboration with CEA Saclay
Vertical test (VT) result (37 MV/m) at CEA Saclay before transportation to KEK /Marui
1AC3 cavity sent from CEA Saclay to KEK / Marui.
VEP + VT plan with 1AC3 cavity
・Inner surface inspection etc.
at Marui
Inner surface
at Marui
(Digital camera)
Marui VEP with “Ninja”
・Transportation back to CEA Saclay.
・Vertical Test (VT) at CEA Saclay
Inner surface
at Marui
(Endoscope)
1AC3 cavity will be VEP’ed at Marui and will be sent back to CEA Saclay for VT.

11. VEP experiments with coupon single-cell cavity
Nb coupons (6 points)
・EP current
・Temperature
・Surface roughness
・Removal thickness
・Impurities
can be investigated.
Coupon cavity
(with 6 Nb coupons and
transparent windows)
Transparent window
(4 points)
・State of bubbles
・State of cathode
can be seen
during VEP process.
VEP condition (an example)
EP solution: H2SO4(98%):HF(55%)=9:1
Voltage: 9–11V
Flow rate: 5L/min
Rotation speed: 1rpm
EP time: 150min
Flow direction: Bottom to top
VEP setup

12. Schematic for a coupon single-cell cavity with a VEP cathode “Ninja”
wing
Upper window
Coupon
Window
Coupon
Lower window
Cathode rod

13. VEP experiment with coupon single-cell cavity
Temperature
(After 120min)
Current density
(After 120min)
Removal thickness
Surface roughness Ra
: Coupon position
Upper
lower
(Temperature near coupon)
The influence of bubble hitting from wings?
(Now under investigation)
・Temperature
Equator is highest
Bubbles
・Current density
・Removal thickness
・Surface roughness Ra
Largest at top iris
To achieve more uniform VEP,
we need to develop how to control bubbles.
EP solution
flow

14. VEP experiment with 9-cell cavity
VEP setup for 9-cell cavity
Degassing tank
9-cell cavity
VEP condition (an example)
EP solution
tank
EP solution: H2SO4(98%):HF(55%)=9:1
Voltage: 7-9V
Flow rate: 10L/min
Rotation speed: 1rpm
EP time: 90min
Flow direction: Bottom to top
Water
Waste
liquid
Schematic view of VEP setup

15. VEP experiment with 9-cell cavity
Upper
Upper
Logged data (Temperature-time)
Lower
Lower
Total average
18.2μm
Temperature in EP tank
Average temperature
of each cell (After 60min)
Average removal thickness
of each cell
Logged data
(Voltage, Current density-time)

16. VEP experiments with 9-cell cavity
Inner surface inspection
From upper side
5th cell upper iris
5th cell equator
Temperature of
each parts (after 60min)
Removal thickness of
each parts
5th cell lower iris
5th cell – 6th cell
We need more optimization (voltage, flow rate, temperature etc.)
→After optimization, we would like to perform vertical test of 9-cell cavity

17. COI: Center-of-Innovation Building at KEK
2012 supplementary-budget: model facility for ILC assembly & Testing
STF building
COI building construction area
COI building

18. COI: Center-of-Innovation Building
As a model facility for ILC assembly & Testing
Clean-room
He Cryogenics
EP(vertical-EP)
Cavity Testing(4-cavities-test)
Cryomodule Assembly(cantilever)
Cryomodule Testing
Cantilever
Vertical-EP

19. New VEP setup delivered for COI building
Cathode motor
EP bed is used both for HEP and VEP (2 ways). This enables the direct comparison of HEP and VEP processes.
Cathode insertion tool.
EP bed
Manufacturer is MHI

20. Summary
KEK started the R&D of Vertical EP (VEP) process in collaboration with Marui Galvanizing Co. Ltd.
Special cathode “Ninja” is developed by Marui Galvanizing Co. Ltd. for VEP process. The “Ninja” cathode has retractable-wings which realize uniform flow of electrolyte and uniform distribution of electric current.
VEP experiments are performed with single-cell cavities, single-cell coupon cavity, and 9-cell cavities to optimize the parameters.
Single-cell cavity “1AC3” provided by CEA Saclay will be VEP’ed with “Ninja” cathode and the cavity will be VT’ed at CEA Saclay.
New COI building will be equipped with VEP/HEP compatible setup by MHI, which was already delivered to KEK. The setup will be installed into the new COI building in 2015.