1. KEK Status and plans of structure production and testing
LCWS at Morioka
8 December 2016
Toshi Higo, KEK

2. Contents Overview of high-gradient testing status at Nextef
High gradient test result
K1 vs K2
Structure production status
S-band activity
Future plans and conclusion
2016/12/8
Higo, LCWS, Morioka

3. High-gradient testing status at Nextef
Overview of high-gradient testing status at Nextef
High gradient test result
K1 vs K2
Structure production status
S-band activity
Future plans
2016/12/8
Higo, LCWS, Morioka

4. Nextef
2016/12/8
Higo, LCWS, Morioka

5. Nextef-A and Nextef-B A B Two klystrons KT1 klystron | | WR90 WR90
10m-long transport
Low-loss wave guide
Shield-A
TW cavity B
KT1 klystron |
WR90
35m-long transport
Low-loss wave guide
Shield-B
SW cavity
2016/12/8
Higo, LCWS, Morioka

6. Fabrication and test of prototype structures T18 Quad  TD18T24TD24TD24R05TD24R05 T24THUTD24R05 Deflector TD24R05
TD24R05_K1
2015
T18_Disk_#2
2009
T24THU_#1
Deflector (SINAP)
2016
TD24R05_#4
TD24R05_K2
2016
TD18_Disk_#2
2010
T24_Disk_#3
2011
TD24R05_#2
2012
TD24_Disk_#4
2016/12/8
Higo, LCWS, Morioka

7. High-gradient test on prototype structures at Nextef
Single-cell SW
TD24R05 #2
TD24_Disk_#4
High power components test
KT1 to shield-B
TD24R05_K1
Replace klystron
T18_Disk_#2
TD18_Quad_#5
TD18_Disk_#2
Narrow waveguide test
KT1
Nextef shield-A
KX03 (60cm HDDS)
T24_Disk_#3
Nextef shield-B
CLIC prototype tests
GLC 1 2 3 4 5
1.5 6
TD24R05 #4
Klystron repair
T24_THU_#1 7 8 9
SINAP Deflector
TD24R05_K2 10
THU Choke-mode SW
T24_K1
Quad SW
2016/12/8
Higo, LCWS, Morioka

8. Recent tests in Nextef TW structures in Shield-A
CLIC prototype T24_THU_#1  Wu
CLIC prototype TD24R05-K1
SINAP deflector  Tan
CLIC prototype TD24R05-K2
SW cavities in Shield-B
System established  Abe
Tsinghua-made cavities focusing choke-mode cavity  Wu
G1.68
G2.1
No-choke
2016/12/8
Higo, LCWS, Morioka

9. T24_THU_#1 High gradient features
Normalized gradient
𝐸∝ 𝑡 𝑝𝑢𝑙𝑠𝑒 − 1 6 ∗ 𝐵𝐷𝑅 1 30
𝐸 ∗ =𝐸⋅ 𝑡 𝑝𝑢𝑙𝑠𝑒 252𝑛𝑠 ∙ 𝐵𝐷𝑅 2× 10 −5 𝑏𝑝𝑝 − 1 30
Normalize to 252ns, 2e-5 bpp
BDR calculated by last 10M pulses
2016/12/8
Higo, LCWS, Morioka

10. Two TD24R05 structures, K1 & K2 CLIC nominal prototype
Same design and almost same manufacturing
Single difference in with/without vacuum baking process
Study high-gradient performance related to hydrogen concentration in copper body
2016/12/8
Higo, LCWS, Morioka

11. Test with SW cavity at B High gradient study in simpler geometry
Aim
Study with single-cell SW cavity
Elaborate evaluation at or on the way to reach the nominal operation level of CLIC, 100 MV/m
Status
Started with choke-mode cavity
BD identification methods were developed and still being developed
Test cavities
Two choke-mode G1.68, G2.1 made by Tsinghua
Frequent breakdowns below 100 MV/m without current flush
Followed by undamped one made by Tsinghua
Is running at over than 100 MV/m
Many others are waiting for test
Quadrant, then brazed, waveguide damped, …..
2016/12/8
Higo, LCWS, Morioka

12. Identification of breakdowns Three trigger logics on reflected wave in addition to current flush
Usual pulse shapes
(normal pulse)
Transmission wave
Reflected wave
Input wave
To be used at Nextef/Shield-B
--- Input wave (envelope)
--- Reflected wave (envelope)
--- Transmission wave (envelope)
“Overall Threshold”
“Pulse Width”
“Number of Edge” (N>=3)
2016/12/8
Higo, LCWS, Morioka

13. High gradient test result: K1 vs K2
Overview of high-gradient testing status at Nextef
High gradient test result
K1 vs K2
Structure production status
S-band activity
Future plans
2016/12/8
Higo, LCWS, Morioka

14. K1 Nominal type TD24R05 for high gradient evaluation
Cells and coupler parts were made by K-pro, a vendor of this Tohoku area.
Cleaned and assembled by and at KEK
Diffusion bonded and brazed, all in hydrogen
Skip vacuum baking process
Tested at Nextef
2016/12/8
Higo, LCWS, Morioka

15. Not so clean environment
TD24R05-K1: Installation as usual carefully done to avoid dust migration but not perfect!
Not so clean environment
Al foils with N2 flow
2016/12/8
Higo, LCWS, Morioka

16. TD24R05－K1 History Tuning completed Thu. 17 Sep.
Installation Fri. 25 Sep.
Processing start Mon. 5 Oct., 2015
Finish 51ns run reaching 105MV/m 11 Nov.
91ns – 132ns – 173ns – 213ns 14 Dec.
252ns ~1400hrs Jan. 2016
412ns run ~2000hrs 18 – 25 Feb. 2016
110 mV/m ~2440hrs March 2016
Finish test after total 3000 hours 7 Apr. 2016
2016/12/8
Higo, LCWS, Morioka

17. Whole trend of TD24R05-K1
2016/12/8
Higo, LCWS, Morioka

18. TD24R05_K1 Instantanuous BDR and BD cell population
2016/12/8
Higo, LCWS, Morioka

19. BDR normalized to 100MV/m, 252nsec
Sophisticated checking/confirmation to count BDR is still to be made.
Error bars are only statistical ones.
Error bar for no ACC-BD case is made by assuming 1 ACC-BD for error bar use.
Fitting is done with five points appeared in this plot.
2016/12/8
Higo, LCWS, Morioka

20. Conclusion on TD24R05-K1 Processed for 3000 hours
Reached up to 110MV/m at 252nsec
Processed up to 412nsec
No hot cell appeared
Moderate dark current, 10 microA at 95 MV/m
Low breakdown rate, <10 -7 bpp/m if scaled to 100MV/m, 252ns
BDR evolution in time, kept decreasing
It showed good performance in high gradient
Indicating that the vacuum baking process is not must
2016/12/8
Higo, LCWS, Morioka

21. K2 Nominal type TD24R05 for high gradient evaluation
Cells and coupler parts were made by Morikawa, our nominal vendor.
Cleaned and assembled by and at KEK
Diffusion bonded and brazed, all in hydrogen
Vacuum baking at vacuum furnace in MHI
Being tested at Nextef
2016/12/8
Higo, LCWS, Morioka

22. TD24R05－K2 History Tuning completed Feb., 2016 Installation Jun., 2016
Processing start 16 Sep, 2015
51ns 10MV/m 7 Oct., 2016
91ns – 132ns – 173ns – 213ns 26 Oct., 2016
252ns ~400hrs 21 Nov., 2016
100  110 MV/m Today
BDR evaluation vs Eacc 18 – 25 Feb. 2016
412ns & various specific study March 2017?
2016/12/8
Higo, LCWS, Morioka

23. 2016/12/8
Higo, LCWS, Morioka

24. 2016/12/8
Higo, LCWS, Morioka

25. 2016/12/8
Higo, LCWS, Morioka

26. Comparison between K1 and K2
2016/12/8
Higo, LCWS, Morioka

27. Ramping pattern vs time or vs #ACC-BD
To be plotted
2016/12/8
Higo, LCWS, Morioka

28. K2 seems behaved better than K1 in BDR
Vacuum baking makes better!?
In order to conclude, we need careful checking/calibration
2016/12/8
Higo, LCWS, Morioka

29. Structure production status
Overview of high-gradient testing status at Nextef
High gradient test result
K1 vs K2
Structure production status
S-band activity
Future plans
2016/12/8
Higo, LCWS, Morioka

30. Preparation of K1 and K2
2016/12/8
Higo, LCWS, Morioka

31. Then KEK-made damped structure TD24R05-K1 Hydrogen furnace-based without baking
K1: Skip baking
2016/12/8
Higo, LCWS, Morioka

32. Background behind tests of K1 and K2
60cm X-band TW’s, ATF-based gun cavities
Former at 500C for a week, or latter without
But behaves reasonably well in high gradient K1
Establish KEK-made CLIC prototype structure
Test structure without high-temperature (>500C) baking
Too costly to follow the baking at 650C for a week K2
Follow K1 technology except for the final baking process
Baking at 750C for a day
Will be determined not only scientifically but also from cost
Compare the high gradient performance w.r.t. K1
2016/12/8
Higo, LCWS, Morioka

33. Comparison among manufacturing technologies SLAC/KEK, KEK-60cm, Tsinghua, KEK-K1, KEK-K2
Features on manufacturing technologies and others
SLAC/KEK
CERN
KEK 60cm
Tsinghua K1 K2
Year
~2000
~2010
~2004
2014
2015
2016
Bonding H2
H2 / Vac
Proceed
SLAC
KEK (Toshiba)
KEK
(MHI-MS)
Baking method
Vacuum can 
Double evacuation -
In vacuum furnace
Parameters
650C
1 week
 ?
500C
5 days
non
~750C
1 day
2016/12/8
Higo, LCWS, Morioka

34. Production record of K1 & K2
TD24R05 K1 K2
Comment
Cell maker
K-PRO
Morikawa
Cell production
May 2011
Mar. 2013
Storage
Desiccator, Air
At KEK
Stack measurement
Dec. 2011
Nov. 2015 CP
May 2014
Dec. 2015
Modified SLAC recipe
DB & Brazing
June 2014
Jan. 2016
Tuning
Sep. 2015
Feb. 2016
Baking
Non
Mar. 2016
750C, 1day at MHI-MS N2
Installation
Jun. 2016
Processing
Oct
Sep
2016/12/8
Higo, LCWS, Morioka

35. K2 manufacturing Machining by Morikawa Tune at KEK
Baking in vacuum furnace at MHI with ports covered by copper foil
CP at KEK DB
Braze
All by KEK hydrogen furnace
2016/12/8
Higo, LCWS, Morioka

36. K2 vacuum baking Main body DB in 1atm (or 1Torr) H2 at 1040C
Coupler with gold braze 1020C
H2 braze for all parts at ~980C
Tuning in clean room.
High temperature vacuum baking
Cooling down without gas circulation
Mildly purge and take out to clean place to be sealed.
Copper foil.
Support
Coupon
2016/12/8
Higo, LCWS, Morioka

37. 800km travel for baking 750degC, 1day treatment
5 x 10-6 Pa
750 C
2016/12/8
Higo, LCWS, Morioka

38. Hydrogen removal feature to get the same diffusion length w. r. t
Hydrogen removal feature to get the same diffusion length w.r.t. 650C and a week
Originally thought
650C  800C makes big change in diffusion length, however,
Diffusion length does not become so high
2 sqrt(D t)  only SLACX1.5, TsinghuaX2.5
Raising temperature to 800C
Intuitively thought parameter 6 hours  90 microns
SLAC：650C、10days  2400 microns
Tsinghua U.: 500C, 5 days 720 microns
K2~Tsinguha X (1/8), SLAC X (1/30)  no good
2016/12/8
Higo, LCWS, Morioka

39. Compromised parameters for large hydrogen diffusion and less copper sublimation
Temperature not so sensitive to diffusion
High temperature gives more sublimation, more sensitive to temperature (900C, 1 hour  1 micron)
Need to find some parameters
A bit lower temperature but longer period
Compromise with cost:
750C, 1 day
2016/12/8
Higo, LCWS, Morioka

40. Worries on surface change due to vacuum furnace treatment
2016/12/8
Higo, LCWS, Morioka

41. We know surface changes in vacuum furnace
Particles
counting, suppression method?
Surface crystal-originated features
When these features are developed?
How much do we need to suppress these?
DB at 1040 degC in 1 Torr H2 for 1 hour, followed by 800C vacuum bake for half an hour,
and ending with N2 purging at 600 degC for cooling by gas circulation.
2016/12/8
Higo, LCWS, Morioka

42. Accompanying coupon in hydrogen furnace stages for K2 production
Bonding process at the hydrogen furnace at KEK
Smooth but very small objects were observed.
Mostly only copper can be observed by SEM-EDX.
Rare case but observed Si, Ca and O.
2016/12/8
Higo, LCWS, Morioka

43. Even in a well-cleaned vacuum furnace
Mn, S and a little Cr.
Baking vacuum furnace
Many objects were observed in the process with very clean furnace by eye
Al and O was detected in the area with the appearance sprayed with white powder
2016/12/8
Higo, LCWS, Morioka

44. Mn x-S y Surrounded by health crystal face melt in or precipitated
2016/12/8
Higo, LCWS, Morioka

45. Al xO y a few to several microns
Sitting on ?
Nominal crystal face
Perturbed surrounding
Thin coating
Sit on copper surface with associated perturbed surrounding area
2016/12/8
Higo, LCWS, Morioka

46. EDX analysis on those foreign substances
2016/12/8
Higo, LCWS, Morioka

47. On-going structure production
TD26CC-K1
Under RF checking with clamped
Should be ready by next March
T24-K1, K2, K3
Under manufacturing parts at Morikawa by next March
Assembly at KEK and treatment in mind
K1 bonded in hydrogen at KEK
K2 the same but followed by MHI baking, 750C, 24hr
K3 the same but followed by CERN baking, 650C, several days
2016/12/8
Higo, LCWS, Morioka

48. Applying idea and methods to our nominal S-band activity
Overview of high-gradient testing status at Nextef
High gradient test result
K1 vs K2
Structure production status
S-band activity
Future plans
2016/12/8
Higo, LCWS, Morioka

49. Modulator voltage Es status as of Oct. 2016 2016/12/8
Higo, LCWS, Morioka

50. Possible causes to be considered
More than 35 year operation with
Many-time changes of linac configuration
Poor vacuum protocol?  poor purging, exposure to air,
Non-heat-treated copper  possibly better?
High energy beam shower?
Need to replace bad structures
Need to develop new-made structures for spares
Want to evaluate and select still-good structures based on X-band developed ideas and experience
2016/12/8
Higo, LCWS, Morioka

51. S-band structure test area developed
We converted S-band test system for X-band 10 years ago.
Now making new S-band test setup independently.
Abrupt jump of reflection at the breakdown event
Stopping next pulse
BD positioning, missing energy, normalized gradient, breakdown rate, etc.
2016/12/8
Higo, LCWS, Morioka

52. Look VSWR statistics Monitoring VSWR statistical features
In some pulses, VSWR abruptly jump
We want to study these statistical features
Time
VSWR
Monitoring VSWR statistical features
VSWR distribution
2016/12/8
Higo, LCWS, Morioka

53. Future plans and conclusion
Prototype structures
TD24R05-K2 under test
T24 or other will follow
Single-cell SW cavities
System established and choke-mode related cavities under test
BD identification is still being developed
Many cavities are waiting  need to better/faster test protocol
Manufacturing
TD26CC are under clamp tested before bonding
Three T24’s are being made
We try to keep the high gradient activity in KEK by
Keep high gradient study on CLIC prototypes as our basic activity
Explore studies with single-cell SW cavities
I hope X-band application studies should be established in KEK.
Probably 1-2 years later, after establishing stable SuperKEKB injection.
Extend X-band to S-band structure development and testing
2016/12/8
Higo, LCWS, Morioka