High power test results of X-band deflecting cavity Jianhao Tan, - - PowerPoint PPT Presentation
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 Outline Background Brief introduction of deflector Conditioning history Breakdown
Jianhao Tan, Wencheng Fang, Qiang Gu, Zhentang Zhao, SINAP Toshiyasu Higo, KEK
Outline
Background Brief introduction of deflector Conditioning history Breakdown position analysis results Summary
SXFEL Test facility linac layout
X-band
Oil tank LLRF
A/D Feedback, Feedforward Set point …… D/ASSA 23MW，0.5us load Load Load 50MW, 100ns 11424MHz
0.6m 0.6m
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
including 6 deflecting structures, each is 60 cm long.
deflecting structures will used on HXFEL (hard x-ray free electron lasers), 1 meter long for each structure.
Scheme 1：Cave type Scheme 2：Hole type Working mode Non-working mode Working mode Non-working mode Two holes (LOLA Structures) Two caved-ins
t (m m) Transverse shut impedance(MΩ/m ) Group velocity( %c) Q value Attenuatio n factor(1/m ) 2.2 45.62 3.17 6345 0.595 2.0 49.07 3.17 6778 0.557 1.8 50.31 3.16 6965 0.544 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
Filling time tF 23 ns a (a/b) (mm) Group velocity (%c) Transvers e shut impedanc e (MΩ/m) Quality factor Attenuati
(1/m) 5.5(0.37)
38.35 6662 0.730 5.2(0.35)
42.24 6622 0.606 5.0(0.34)
46.04 6778 0.564 4.5(0.30)
54.09 6924 0.543 4.0(0.26)
61.53 7072 0.646 3.5(0.23)
68.81 7821 0.757
With caves on outside wall of the cups to fix the direction.
Cave
The machining model of couplers, with box and cover, and an regular cup attached to the coupler box.
Cover Box Box with regular cup
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)
Layout of Deflector
SINAP_DEF
4 stages operation
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 50MW @173ns. 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.
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
For accelerating structures For deflecting structure
const BDR t E
p a
5
30
𝐹𝑒𝑓𝑔=
𝑊𝑒𝑓𝑔 𝑀
𝐹𝑒𝑓𝑔
𝐶𝐸𝑆 = 𝑑𝑝𝑜𝑡𝑢
Operation start from 14 April @51ns 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.
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.
33MW 30MW
Operation start from 9 May @ 91ns Power target set 40MW 6~7 days increase power up to 40MW, no breakdown rate evaluation
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
12 hours 25 breakdowns
Run#24 analysis results Power keep at 43MW @173ns 20 breakdowns record during 1215 minutes, about 20 hours BDR= 5.49 *e -6
Run#25 analysis results Power keep at 41MW @173ns 25 breakdowns record during 2678 minutes, about 45 hours BDR= 3.11 *e -6
KEK program
Instead of deflector parameters 𝐺 𝑨 = 2𝑨 𝑊 − 𝑀 𝑊
2
𝐺 𝑨 = ∆𝑆𝑡 − ∆𝑈𝑠 − 𝑈
𝑔𝑗𝑚𝑚
(∆𝑆𝑡−∆𝑈𝑠−𝑈𝑔𝑗𝑚𝑚)𝑊+𝑀 2
(∆𝑆𝑡−∆𝑈𝑠−𝑈𝑔𝑗𝑚𝑚)𝑊+𝑀 2
𝑈
𝑔𝑗𝑚𝑚 = 𝑀
𝑊
(∆𝑆𝑡−∆𝑈𝑠)𝑊 2
𝐺 𝑨 = න
𝑨 𝑒𝑨
𝑤
− න
𝑨 𝑀 𝑒𝑨
𝑤
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.
Run#10 Run#17 Population of breakdown cell as processing ▽ △◇ □○ Lots of breakdowns in upstream cells Further processing, appeared breakdowns in the downstream 132ns Running Take 132ns running as an example Suspected that the breakdowns resulted by leaking of alloy into the structure
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 Disk
Coupler aperture Location of leaking @ first brazing
coupler Image under optical microscope, it is
that the positions in the upstream and downstream where breakdown frequently are concentrated in the coupler aperture. More analysis will carry
in scanning electron microscope.
Damaged heavily
Results under optical microscope
Input side Output side Disks from upstream and downstream
1mm