1. Recent results of Vertical-EP at KEK-Marui
LCWS2017 SRF-WG H. Hayano-KEK
Recent results of Vertical-EP
at KEK-Marui
Hitoshi Hayano (KEK) for
Keisuke Nii, Vijay Chouhan, Yoshiaki Ida, Takanori Yamaguchi, Kiyotaka Ishimi, Atsushi Toose　
(Marui Galvanizing Co., Ltd.)
Hitoshi Hayano, Shigeki Kato, Hideaki Monjushiro, Takayuki Saeki, Motoaki Sawabe,
(High Energy Accelerator Research Organization (KEK))
Hiroki Oikawa　(Utsunomiya University)
Hayato Ito (The Graduate University for Advanced Studies: Sokendai)
G. Mitoya, T. Akabori, K. Miyano, F. Takahashi, Y. Anetai, M. Fijisawa, S. Murakami,
K. Suzuki, K. Kon, K. Omori ( VEP Iwate collaboration )
Fumio Furuta (Cornell), Fabien Eozenou (Saclay)

2. US-Japan Cost-down : A-4. Cavity chemical treatment
The change of the SC-cavity chemical treatment,
from horizontal EP and sulfuric acid + HF (TDR)
to vertical EP (VEP) + non-HF solution + bipolar EP,
will be effective to ILC cost down.
VEP
with
wing-cathode
Bipolar EP
using non-HF solution
ILC EP cost-down
The development of vertical EP (VEP) is the first step.

3. Vertical EP (VEP) for Single-Cell Cavity

4. Wing Cathode (Ninja-cathode) Development
partial metal wing
during
insertion
during EP
Al small
electrode
Al small
electrode
partial metal
wing
metal wing
insulator wing
Flat removal
was attained

5. Roughness Monitoring by coupon cavity
partial metal wing
Viewport
insulator wing
metal wing
smooth surface finish
was attained
partial metal
wing
metal wing
Viewports enable us to look
H2 bubbles generation and flow
insulator wing

6. Single-cell VEP at Marui
motor for cathode rotation
water spray
for cavity outside cooling
partial metal
wing
insulator wing
13-15V, 30mA/cm2, 28degree, 50rpm, 5L/min

7. Recent 1-cell VEP at Marui towards vertical test at KEK
07 September, 2017
* Vertical test was suspended by the accident,
AC-power-down during cool-down, Vac. pressure was increased,
then severe Q-desease happened on 21 Sep
The next vertical test is scheduled in November.

8. Recent Single-cell VEP at Marui
Side View
Top
View
Ninja-5
single-cell cavity with support-jig
Automated EP acid control valves
( VEP Iwate collaboration)
VEP mount

9. Recent Single-cell VEP at Marui
Cavity-top acid reservoir
Cavity-bottom acid reservoir
cost effective ALL PVC-made system ( VEP Iwate collaboration )
EP acid reservoir tank has 5-filtered-room
for H2 bubble erasing: it was effective.
EP acid reservoir tank with water-chiller

10. Recent Single-cell VEP at Marui
before VEP
after VEP
shiny finish surface was attained!!

11. Recent Single-cell VEP at Marui
Average removal　39μm
Flat removal was attained!!

12. Vertical EP (VEP) for 9-Cell Cavity

13. Recent Wing Cathode (Ninja-cathode) for 9-cell
Insulating wings
(3 wings per cell)
Ninja-5
I-V curves of the coupons
Side View
Top Cell
Cathode housing covered with meshed sheet
(catch-up H2 bubbles)
Top Iris
Equator
Bottom Iris
Top
View
Enhanced cathode surface area
(additional Al electrodes)
Center Cell
Top Iris
Equator
Bottom Iris
Parameters
Condition
Acid (H2SO4:HF)
9:1
Acid flow direction
Bottom to top
Acid flow rate
5-7 L/min
Cathode rotation speed
50 rpm
Cathode
Ninja-5
Voltage
~13 V
Current Density
18 mA/cm2
Cavity temperature
15 °C
VEP condition
(Follow the 1-cell VEP
best condition)
Bottom Cell
Top Iris
Equator
Bottom Iris
13V

14. Coupon holders and view ports
Roughness Monitoring by 9-cell coupon cavity
The world’s first 9-cell coupon cavity has been fabricated.
9-cell coupon cavity
Coupon holders and view ports
(Near iris position)
Coupon holder
(Equator position)
In order to optimize VEP parameters, a 9-cell coupon cavity was fabricated.
・ Nb coupons are set on equator positions of 1st, 5th and 9th cell.
・ View ports with Nb coupon are set near iris of 1st, 5th and 9th cell.
・ EP current can be measured for individual coupon.
・ Coupons are removed for surface analysis.

15. Roughness Monitoring by 9-cell coupon cavity
Roughness (Rz)
Microscope images of the coupons
Almost smooth surface were attained, except one location.

16. EP removal thickness of 9-cell coupon cavity
Top View 0°
180°
Average removal: 35 µm
Asymmetry between top
and bottom
(60µm - 30µm)
Still Non-Flat removal
for 9-cell cavity
Cavity was connected to
Automated EP acid control valves

17. Recent 9-cell VEP at Marui towards vertical test at KEK
05 October, 2017
* Vertical test was suspended by the accident,
Vaccum leak happened at RF pickup feedthrough silver-brazing
during 120C baking, on 15 Oct

18. Recent 9-cell VEP at Marui
VEP Conditions
cavity was water-spray cooled
Cathode: Ninja cathode v5 (contains 3 wings in each cell)
Cathode rotation: 20 rpm
Acid flow rate: ~5 L/min
Voltage: ~14-16 V
Cooling:
Acid cooling in acid reservoir using Chiller-1 (5 kW)
Spray of water cooled by chiller-2 (1.2 kW)
Target cavity temperature ~ 15 °C
Target current: 160 A
Target removal thickness: 50 µm
Cavity-top acid reservoir
was filled with bubbles
EP acid reservoir tank
has 5-filtered-room
for H2 bubble erasing,
but still bubbles
were remained in this
9-cell VEP.

19. Surface finish From the Top (Before VEP) From the Top (After VEP)
Input coupler Flange
Bubbles might gathered at the flange of input coupler and made the surface rougher.
HOM cup was also
rough surface.

20. Vertical Tests of VEP 1-Cell Cavities
at Cornell and Saclay

21. Collaborative Study with Cornell and Saclay
Collaborator : Fumio Furuta (Cornell), Fabien Eozenou (Saclay)
( Cornell )
( Saclay )

22. Cathode comparison with Cornell VEP
Cornell-KEK Feb. 2016
VEP at Cornell using Marui-Ninja-cathode
During EP
insertion
Ninja-3
Concept of newly developed Ninja-cathode
(retractable wing for H2 bubbles flow control and acid flow control)
KEK-Marui-Cornell development
1-cell Cavity
VEP
With Ninja-cathode
at Cornell
Right Vertical Test shows,
KEK-VEP (Ninja cathode) has similar
performance with
Cornell-VEP (rod cathode),
reached to 35MV/m.

23. Summary of recent VEP development
VEP setup and unique Ninja cathodes were developed for surface treatment of Nb cavities.
VEP parameters and design of the Ninja cathode were optimized for single cell cavity.
Smooth surface and symmetric removal of Nb along cavity length were obtained with the Ninja cathode.
The Ninja cathodes and optimized VEP parameters were applied to two single-cell cavities which showed good performance in vertical tests performed at Cornell University and CEA-Saclay.
The world’s first 9-cell coupon cavity has been fabricated. VEP parameters are being optimized using the cavity.
Vertical test of 9-cell cavity with VEP & Ninja-cathode was suspended by the feedthrough leak. The reason of leak is now under investigation.

24. End of slide