VEP studies at STF/KEK
T. Saeki (KEK)
15 May 2014
AWLC2014 at FNAL
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.
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)
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
Development of retractable wing-shape cathode in
collaboration with Marui Co. Ltd.
EP electrolyte is circulated to remove
hydrogen gas and for low temperature.
The retractable-wing cathode to realize
uniform flow of electrolyte and uniform
distribution of electric current.
Flow direction
•Side View
Rotation
of cathode
Al
Acid
bath
•Top View
Pump
•Opened
•Retracted
Marui Galvanizing Co. Ltd. named the cathode “Ninja”, which is registered as a trade name.
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
VEP experiment with single-cell cavity
VEP setup
single-cell cavity
(-)
Spot Cooler
Motor
Nb Single
Cell Cavity
(+)
Pump 1
VEP condition (an example)
Pump 2
Acid Container
Heat Exchanger
Schematic view of VEP setup
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
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.
VEP experiment with single-cell cavity
35
60
60
50
50
40
40
30
30
20
20
10
10
Lower beam
pipe
Near the
equator (lower)
Near the
equator (upper)
Upper beam
pipe
Inlet of EP
solution
Outlet of EP
solution
29
27
25
23
21
19
17
15
0
0
20
40
60
80
100
Current density
Voltage
0
0
20
40
60
80
100
Time(min)
Time（ min）
Logged data (Temperature-time)
Upper
cup
40
30
25
20
15
10
5
0
1
2
3
4
5
6
Point of measurement
Polishing amount (μm)
40
Lower
cup
40
1～8
35
Polishing amount (μm)
After VEP
Logged data
(Voltage, Current density-time)
Polishing amount (μm)
Before VEP
Voltage（ V)
Temperature（ ℃）
31
Current density（ mA/cm 2 ）
33
7
8
9～16
35
30
25
20
15
10
5
0
91
2
10
17～24
35
1
30
25
2
20
3
15
4
5
171
2
18
3
4
5
6
19
20
21
22
Point of measurement
7
23
8
24
5
10
18
7
15
16
7
15
8
16
Upper
19
20
21
14
8
In the next step, we would like to do vertical test and know
the acceleration gradient of VEP’ed cavity.
17
12
13
6
Removal thickness
9
11
10
0
Inner surface of cavity
3
4
5
6
11
12
13
14
Point of measurement
22
23
24
Lower
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
VEP + VT plan with 1AC3 cavity
1AC3 cavity sent from CEA Saclay to KEK / Marui.
・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
1AC3 cavity will be VEP’ed at Marui and will be sent back to CEA Saclay for VT.
Inner surface
at Marui
(Endoscope)
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)
VEP setup
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
Schematic for a coupon single-cell cavity with a VEP cathode “Ninja”
Cathode
wing
Upper window
Coupon
Window
Coupon
Lower window
Cathode rod
VEP experiment with coupon single-cell cavity
Temperature
(After 120min)
: Coupon position
20
Upper
Temperature (℃)
22 24 26 28
Current density
(After 120min)
Removal thickness
Current density (mA/cm2)
5 10 15 20 25 30 35
30
Top beam pipe
Top beam pipe
Top iris
Surface roughness Ra
Removal thickness (μm)
30
50
70
90
Surface roughness Ra (μm)
0
110
Top beam pipe
Top beam pipe
Top iris
Top iris
Top iris
Equator left
Equator left
Equator left
Equator left
Equator right
Equator right
Equator right
Equator right
Bottom iris
Bottom iris
Bottom iris
Bottom iris
Bottom beam pipe
Bottom beam pipe
Bottom beam pipe
0.2
0.4
0.6
Bottom beam pipe
lower
(Temperature near coupon)
・Temperature
The influence of bubble hitting from wings?
(Now under investigation)
Equator is highest
・Current density
・Removal thickness
・Surface roughness Ra
Bubbles
Largest at top iris
To achieve more uniform VEP,
we need to develop how to control bubbles.
EP solution
flow
VEP experiment with 9-cell cavity
VEP setup for 9-cell cavity
Degassing tank
9-cell cavity
VEP condition (an example)
EP solution
tank
Water
Waste
liquid
Schematic view of VEP setup
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
VEP experiment with 9-cell cavity
50
U1E
U1LI
45
U2UI
42
U2E
43
Temperature (℃)
44
45
46
47
0
Average removal thickness (μm)
5
10
15
20
25
30
U2LI
40
U3UI
U3E
1
U3LI
U4UI
Temperature (℃ )
35
Upper
1
Upper
U4E
U4LI
U5UI
30
U5E
2
2
3
3
4
4
U5LI
U6UI
U6E
25
U6LI
U7UI
U7E
20
U7LI
U8UI
U8E
15
U8LI
sol
10
0
20
40
60
80
100
120
140
RT
160
Time (min)
Logged data (Temperature-time)
5
5
6
6
7
7
8
8
15
25
20
10
Voltage (V)
Current density (mA/cm2)
30
Cell No.
U9E
Cell position
U9UI
15
10
5
5
9
Lower
9
Temperature in EP tank
0
0
0
20
40
60
Time (min)
80
Lower
Total average
18.2μm
100
Logged data
(Voltage, Current density-time)
Average temperature
of each cell (After 60min)
Average removal thickness
of each cell
VEP experiments with 9-cell cavity
Inner surface inspection
Temperature (℃ )
Point of measurment
Position
U5UI
U5E
U5LI
U6UI
U6E
U6LI
U7UI
U7E
U7LI
U8UI
U8E
U8LI
U9UI
U9E
Temperature of
each parts (after 60min)
70
U4E
U4LI
60
U4UI
50
U3E
U3LI
40
U3UI
30
U2E
U2LI
20
0
U1LI
U2UI
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48
U1E
10
50
49
48
47
46
45
44
43
42
41
40
Removal thickness（ mm）
From upper side
5th cell upper iris
Removal thickness of
each parts
5th cell lower iris
5th cell equator
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
COI: Center-of-Innovation Building at KEK
2012 supplementary-budget: model facility for ILC assembly & Testing
STF building
COI building construction area
COI building
17
COI: Center-of-Innovation Building
Vertical-EP
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
Cantilever18
New VEP setup delivered for COI building
Cathode
motor
Cathode
insertion tool.
EP bed
Manufacturer is MHI
EP bed is used both for
HEP and VEP (2 ways).
This enables the direct
comparison of HEP and
VEP processes.
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 retractablewings 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.