1. High power test results of X-band deflecting cavity
Jianhao Tan, Wencheng Fang, Qiang Gu, Zhentang Zhao, SINAP
Toshiyasu Higo, KEK
June. 15, 2017, Valencia

2. Outline Background Brief introduction of deflector
Conditioning history
Breakdown position analysis results
Summary

3. SXFEL Test facility linac layout
X-band

4. X-Band TDS layout for SXFEL User Facility
Oil tank
LLRF
A/D
Feedback, Feedforward
Set point ……
D/A
SSA
23MW，0.5us
load
Load
50MW, 100ns
11424MHz
Specification of SXFEL user facility：
Energy：1500MeV
Bunch length：76um（RMS）
Beam size：36um
Install space：<1.3 m
Resolution：20fs
Deflecting voltage：30MV
Input power: 20MW
3 dB splitter
0.6m
0.6m

5. Demand of X-Band TDS
1. For now, three RF units of x-band deflecting structures have been confirmed, including 6 deflecting structures, each is 60 cm long.
2. As diagnostic tool and RF kicker, at least 5 units normal conducting x-band deflecting structures will used on HXFEL (hard x-ray free electron lasers), 1 meter long for each structure.

6. Preliminary design of cell shape
Working mode
Two caved-ins
on cell ID surfaces
Non-working mode
Working mode
Non-working mode
Two holes
(LOLA Structures)
Scheme 1：Cave type
Scheme 2：Hole type

7. Optimization of Regular Cells
a (a/b)
(mm)
Group velocity
(%c)
Transverse shut impedance
(MΩ/m)
Quality factor
Attenuation factor
(1/m)
5.5(0.37)
-2.46
38.35
6662
0.730
5.2(0.35)
-2.98
42.24
6622
0.606
5.0(0.34)
-3.17
46.04
6778
0.564
4.5(0.30)
-3.18
54.09
6924
0.543
4.0(0.26)
-2.62
61.53
7072
0.646
3.5(0.23)
-2.02
68.81
7821
0.757
Structure type
Constant impedance
Operating frequency
11.424GHz
Operating mode
Disk-loaded waveguide 2pi/3
Total length L
0.3 m
Resolution
20fs
Deflecting voltage
10MV
Input power
30 MW
Group velocity Vg
-2.62%c
Filling time tF
23 ns t
(mm)
Transverse shut impedance(MΩ/m)
Group velocity(%c)
Q value
Attenuation factor(1/m)
2.2
45.62
3.17
6345
0.595
2.0
49.07
6778
0.557
1.8
50.31
3.16
6965
0.544

8. Fabrication of cells and couplers
Cave
With caves on outside wall of the cups to fix the direction.
Box with regular cup
Cover
Box
The machining model of couplers, with box and cover, and an regular cup attached to the coupler box.

9. Field measurement and tuning results
The cage, with several metal wires surrounded on the carrier which could be scrip or Teflon, the performance affected by Diameter(D) Length(L) metal diameter(b) and Number(N)

10. Nextef A Control Installation on SHIELD-A Shield A RF source for A
SINAP_DEF
Control
Layout of Deflector
Shield A A

11. Conditioning history

12. Operation Plan 4 stages operation 4, April, 2016 30, June, 2016
Power
Pulse width
91 ns
50 MW
2nd
3rd
4th
40 MW
45 MW
35 MW
1st
51 ns
132 ns
173 ns
4, April, 2016
30, June, 2016
Totally conditioning time: nearly three months, but take the holidays and maintain days out, left 8 weeks to test deflector. (Test of TD24R#05 begin July 2016)
The first x-band structure design, fabrication, brazing and test, so we want to test more pulse width, and get more breakdowns information at different width, feed back to the design and technology of fabrication and brazing.
Start from 51ns, final target power is Due to the limit of conditioning time, and worried about lots of time will used on higher power and longer pulse width, so the conditioning process operated as we planed.
Power up to nearly 45 MW, lots of breakdowns prevent power increase. Lots of problems, not bad things.

13. Conditioning history For accelerating structures
For deflecting structure
𝐸 𝑑𝑒𝑓 𝑡 𝑝 5 𝐵𝐷𝑅 =𝑐𝑜𝑛𝑠𝑡
𝐸 𝑑𝑒𝑓 = 𝑉 𝑑𝑒𝑓 𝐿

14. RF Conditioning Results @ 51ns
Operation start from 14
Two weeks running, reach to power 30MW.
On the condition of this power level, meet the requirement of bunch length measurement.
BDR evaluation continue two days running.

15. BDR Evaluation Results @ 51ns
33MW
30MW
Over 35 hours running, 8 breakdowns record at 30 MW. 1.2*e-6 breakdowns per pulse.
11 breakdowns record during 13 hours at 33MW. 4.7*e-6 breakdowns per pulse.

16. RF Conditioning Results @ 91ns
Operation start from 9 91ns
Power target set 40MW
6~7 days increase power up to 40MW, no breakdown rate evaluation

17. BDR Evaluation @ 132ns Run#16 analysis results Power keep at 38MW
12 hours 25 breakdowns
Threshold program error
Run#16 analysis results
Power keep at 38MW
78 Acc-BD record over 62 hours, 1.25 breakdowns happen per hour,7.99*e-6 breakdowns per pulse
About several hours conditioning at 40MW

18. BDR Evaluation @ 173ns Run#24 analysis results
Power keep at
20 breakdowns record during 1215 minutes, about 20 hours
BDR= 5.49 *e -6

19. BDR Evaluation @ 173ns Run#25 analysis results
Power keep at
25 breakdowns record during 2678 minutes, about 45 hours
BDR= 3.11 *e -6

20. Breakdown Position Analysis Results

21. BD position Analysis program-Deflector
KEK program
Instead of deflector parameters
𝐹 𝑧 = 2𝑧 𝑉𝑔 − 𝐿 𝑉𝑔
---> z= 𝐹 𝑧 𝑉𝑔+𝐿 2
𝐹 𝑧 =∆𝑅𝑠−∆𝑇𝑟− 𝑇 𝑓𝑖𝑙𝑙
---> z= (∆𝑅𝑠−∆𝑇𝑟− 𝑇 𝑓𝑖𝑙𝑙 )𝑉𝑔+𝐿 2
---> z= (∆𝑅𝑠−∆𝑇𝑟− 𝑇 𝑓𝑖𝑙𝑙 )𝑉𝑔+𝐿 2
𝐹 𝑧 = 0 𝑧 𝑑𝑧 𝑣 𝑔 − 𝑧 𝐿 𝑑𝑧 𝑣 𝑔
𝑇 𝑓𝑖𝑙𝑙 = 𝐿 𝑉𝑔
---> z= (∆𝑅𝑠−∆𝑇𝑟)𝑉𝑔 2

22. Breakdown Position Analysis Results
Different pulse width operation have the same trend, all have two “hot spot” in the up and downstream;
Divide the structure into three parts, middle parts, upstream parts and downstream parts.
In the middle parts, the number of breakdown almost the same each cell.
A few of breakdowns out of range of structure, accuracy of the breakdown position from program is not enough, need more analysis.
Lots of breakdowns happen in the upstream and downstream of the structure, not reasonable.

23. Breakdown Position Analysis Results
132ns Running
Run#10
Take 132ns running as an example
Run#17
Population of breakdown cell as processing
▽ △◇ □○
Lots of breakdowns in upstream cells
Further processing, appeared breakdowns in the downstream
Suspected that the breakdowns resulted by leaking of alloy into the structure

24. Cutoff analysis-cut view
Disk
Coupler aperture
Location of first brazing
Cutting view of deflector, and made several samples to observe in the optical microscope and SEM;
The dirty things in the cavities, they are not caused by breakdown. Liquid with acid to clean the cavity after wire-cutting

25. Image under optical microscope
Results under optical microscope
Image under optical microscope, it is obvious that the positions in the upstream and downstream where breakdown frequently are concentrated in the coupler aperture.
More analysis will carry out in scanning electron microscope.
coupler
Damaged heavily
Input side
Disks from upstream and downstream
Output side

26. Test results to design
1mm
The test results show that the frequently breakdown in the coupler prevent the higher power running.
Optimization of coupler will used on new deflector design.

27. Summary
The first prototype of x-band deflecting structure has been finished, including design, fabrication, brazing, test, tuning and high power test……
Have found some problems of fabrication and brazing, analysis about BD position, such as cut structure to halves have done and the analysis results basically reflected the problem of design.
Optimization of coupler will used on new deflector design.

28. Thank you!!!

29. Acknowledgement Many thanks to…
T. Higo, S. Matsumoto, T. Abe, A. Karube, A. Asai,
Kawaba, Y. Arakida, T. Takatomi, P. Matsui,
X. Wu…
and many other members of KEK contribute to SINAP Deflector test.