Laser-triggered RF breakdown experiment with a photo-cathode RF gun at Tsinghua University
description
Transcript of Laser-triggered RF breakdown experiment with a photo-cathode RF gun at Tsinghua University
![Page 1: Laser-triggered RF breakdown experiment with a photo-cathode RF gun at Tsinghua University](https://reader036.fdocuments.us/reader036/viewer/2022062323/5681629e550346895dd3147f/html5/thumbnails/1.jpg)
Laser-triggered RF breakdown experiment with a photo-cathode RF gun at Tsinghua University
Presented on behalf of the collaboration byJiaru Shi
Department of Engineering Physics, Tsinghua University
2013.06.04 HG2013, Trieste, Italy
![Page 2: Laser-triggered RF breakdown experiment with a photo-cathode RF gun at Tsinghua University](https://reader036.fdocuments.us/reader036/viewer/2022062323/5681629e550346895dd3147f/html5/thumbnails/2.jpg)
Acknowledgement• Tsinghua University
– Yingchao Du, Jiahang Shao, Lixin Yan, Jianfei Hua, Zhen Zhang, Dan Wang, Jin Yang, Chuanxiang Tang, Huaibi Chen, Wenhui Huang and et. al.
• ANL– Wei Gai, Chunguang Jing
• SLAC– Faya Wang
![Page 3: Laser-triggered RF breakdown experiment with a photo-cathode RF gun at Tsinghua University](https://reader036.fdocuments.us/reader036/viewer/2022062323/5681629e550346895dd3147f/html5/thumbnails/3.jpg)
Content
• Pre-experiment• Experiment setup• Data Analysis• Problems and Plans
![Page 4: Laser-triggered RF breakdown experiment with a photo-cathode RF gun at Tsinghua University](https://reader036.fdocuments.us/reader036/viewer/2022062323/5681629e550346895dd3147f/html5/thumbnails/4.jpg)
Motivation
• RF breakdown dependence on E, B, Sc, ΔTp...– Laser assistant RF breakdown experiment is trying to
isolate some of the contributing effects. Hopefully, a more coherent picture of RF breakdown. [1]
• RF breakdown phenomenon– To better understand detailed RF breakdown progress
and time scale. Quantities like turn on time, breakdown current, explosive emission… [2]
[1] Faya Wang[2] Wei Gai, Chunguang Jing
![Page 5: Laser-triggered RF breakdown experiment with a photo-cathode RF gun at Tsinghua University](https://reader036.fdocuments.us/reader036/viewer/2022062323/5681629e550346895dd3147f/html5/thumbnails/5.jpg)
Pre-Experiment: Laser damage on copper surface
• Shot UV Laser pulse on copper surface.– 10μJ, 20, 30…; 1mm diameter spot size; 1ps pulse length– Microscope image: (30sec@10Hz)
60 μJ 30 μJ
![Page 6: Laser-triggered RF breakdown experiment with a photo-cathode RF gun at Tsinghua University](https://reader036.fdocuments.us/reader036/viewer/2022062323/5681629e550346895dd3147f/html5/thumbnails/6.jpg)
Laser damage
10μJ 20μJ 30μJ
40μJ 50μJ 60μJ Surface damage
oxidization
10μJ / 1mm^2 0.1 J/cm^2 @1ps 10GW/cm^2
![Page 7: Laser-triggered RF breakdown experiment with a photo-cathode RF gun at Tsinghua University](https://reader036.fdocuments.us/reader036/viewer/2022062323/5681629e550346895dd3147f/html5/thumbnails/7.jpg)
Schematic of the Beamline• laser
– Laser: Ti:Sapphire, 800nm, 400nm and 266nm
– 90 degree incident – Pulse duration: ~1ps– Max Energy: ~2mJ
• 1/3 to cathode from clean room
– Energy jitter: ~5%
![Page 8: Laser-triggered RF breakdown experiment with a photo-cathode RF gun at Tsinghua University](https://reader036.fdocuments.us/reader036/viewer/2022062323/5681629e550346895dd3147f/html5/thumbnails/8.jpg)
RF gun at Tsinghua• RF Source
– 5MW klystron• RF Gun
– 1.6-cell S-band 2856MHz– Solid, demountable Cu
back-plate– Q~6000– 30~50MV/m
![Page 9: Laser-triggered RF breakdown experiment with a photo-cathode RF gun at Tsinghua University](https://reader036.fdocuments.us/reader036/viewer/2022062323/5681629e550346895dd3147f/html5/thumbnails/9.jpg)
Beamline
1 2 3 4
a=53cmb=85cm
gun laser hole Faraday cup
oscilloscope
Scope: 12GHz Bandwidth / 50GHz sampling rate
![Page 10: Laser-triggered RF breakdown experiment with a photo-cathode RF gun at Tsinghua University](https://reader036.fdocuments.us/reader036/viewer/2022062323/5681629e550346895dd3147f/html5/thumbnails/10.jpg)
Scope signal w/ and w/o breakdown
0 500 1000 1500 2000 2500 3000 3500 4000-2
0
2RF pickup
0 500 1000 1500 2000 2500 3000 3500 4000-1
0
1Reflection
0 500 1000 1500 2000 2500 3000 3500 4000-0.2
0
0.2Photodiode
0 500 1000 1500 2000 2500 3000 3500 4000-5
0
5
Time (ns)
Faraday cup
0 500 1000 1500 2000 2500 3000 3500 4000-2
0
2RF pickup
0 500 1000 1500 2000 2500 3000 3500 4000-1
0
1Reflection
0 500 1000 1500 2000 2500 3000 3500 4000-0.2
0
0.2Photodiode
0 500 1000 1500 2000 2500 3000 3500 4000-5
0
5
Time (ns)
Faraday cup
RF pickup
Reflection
Photo Diode
Faraday Cup
Time aligned ~1ns
![Page 11: Laser-triggered RF breakdown experiment with a photo-cathode RF gun at Tsinghua University](https://reader036.fdocuments.us/reader036/viewer/2022062323/5681629e550346895dd3147f/html5/thumbnails/11.jpg)
ExperimentApr 12 Apr 18 Apr 19
p1 p2 p3 p4 p5 p6 p7Laser Energy @ cathode
(μJ)Scan
up to 135μJ55 150 100 117 128
Input Power (MW)
4.3MW Scan 2-5MW
E field (MW/m)
50MV/m 30-50MV/m
Change location on cathode: (p1, p2, p3)
RF phase fixed 30 degree.
Image after experiment (view from oblique-incident laser window)
![Page 12: Laser-triggered RF breakdown experiment with a photo-cathode RF gun at Tsinghua University](https://reader036.fdocuments.us/reader036/viewer/2022062323/5681629e550346895dd3147f/html5/thumbnails/12.jpg)
90 95 100 105 110 115 120 125 130 135 1400
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
point 1point 2
Laser energy on cathode (uJ)
Brea
kdow
n pr
obab
ility
Breakdown rate v.s. Laser Energy
• E at center of cathode ~50MV/m, note: small statistics
![Page 13: Laser-triggered RF breakdown experiment with a photo-cathode RF gun at Tsinghua University](https://reader036.fdocuments.us/reader036/viewer/2022062323/5681629e550346895dd3147f/html5/thumbnails/13.jpg)
Charge v.s. Laser Energy and E-field
25 30 35 40 45 50 55 6030
40
50
60
70
80
90
100
4.18 55uJ4.18 150uJ4.19 117uJ4.19 128uJ
E on cathode surface (MV/m)
Char
ge (n
C)
Charge strongly-related to E field
Different Laser energy? Maybe: from different location
![Page 14: Laser-triggered RF breakdown experiment with a photo-cathode RF gun at Tsinghua University](https://reader036.fdocuments.us/reader036/viewer/2022062323/5681629e550346895dd3147f/html5/thumbnails/14.jpg)
Timing (cables calib.’ed)
0 1000 2000 3000 4000-1
0
1
2
3
4
t (ns)
Far.CupReflectionDiodeRF pickup
0 1000 2000 3000 4000-1
-0.5
0
0.5
1
1.5
2
t (ns)
Far.CupReflectionDiodeRF pickup
w/o breakdown
w/ breakdown
1180 1200 1220 1240 1260 1280 1300 1320
0
0.5
1
1.5
2
2.5
3
3.5
t (ns)
Far.CupReflectionDiodeRF pickup
after photo-electron: Breakdown current rises ~ns Reflection starts to change ~40ns RF pickup increase because of beam excitation
![Page 15: Laser-triggered RF breakdown experiment with a photo-cathode RF gun at Tsinghua University](https://reader036.fdocuments.us/reader036/viewer/2022062323/5681629e550346895dd3147f/html5/thumbnails/15.jpg)
Take Faraday cup as an LTI system.signal without breakdown can be seen as the impulse response of the system.Try to solve the ‘real’ current signal by deconvolution.
Hδ(t) h(t)
Hδ(t)+b(t) y(t)
δ(t) : impluse functionb(t) : ‘real’ breakdown currenth(t) : Faraday cup signal without breakdowny(t) : Faraday cup signal with breakdown
1160 1180 1200 1220 1240 1260 1280 1300 1320-1
-0.5
0
0.5
1
Time (ns)
Current (A
)
h(t)
1160 1180 1200 1220 1240 1260 1280 1300 1320-2.5
-2
-1.5
-1
-0.5
0
0.5
Time (ns)
y(t)
Current (A
)
Data ProcessingJ. Shao
![Page 16: Laser-triggered RF breakdown experiment with a photo-cathode RF gun at Tsinghua University](https://reader036.fdocuments.us/reader036/viewer/2022062323/5681629e550346895dd3147f/html5/thumbnails/16.jpg)
• Time: Rise time ~15ns, flattop ~35ns, ~5ns (fast) turn-off• Charge: Photo-electron ~100pC, breakdown (collected) ~30nC
0 10 20 30 40 50 60 70 80-0.25
-0.2
-0.15
-0.1
-0.05
0
0.05
0.1solved x^
Time (ns)
“real” breakdown current (by de-convolution)J. Shao
![Page 17: Laser-triggered RF breakdown experiment with a photo-cathode RF gun at Tsinghua University](https://reader036.fdocuments.us/reader036/viewer/2022062323/5681629e550346895dd3147f/html5/thumbnails/17.jpg)
Plans and discussion
• Different laser wavelength• Missing Energy? • Update Faraday Cup eliminate resonance, better
matching, faster time response• Streak Camera Diagnostics of the breakdown current,
micro structure?
![Page 18: Laser-triggered RF breakdown experiment with a photo-cathode RF gun at Tsinghua University](https://reader036.fdocuments.us/reader036/viewer/2022062323/5681629e550346895dd3147f/html5/thumbnails/18.jpg)
Summary and discussion
• Very preliminary data analysis– charge (? get real breakdown current)– (Rough) delay time, turn one time– Laser threshold
• Laser-triggered RF breakdown v.s. self-breakdown, • v.s. DC breakdown?• Suggestions?