1. STREAK CAMERA 101 − Visualizing charged-particle beam dynamics
4/22/2017
STREAK CAMERA − Visualizing charged-particle beam dynamics
Beam Instrumentation Workshop – May 3, 2006
Bingxin Yang
ASD/DIAG, Advanced Photon Source, Argonne National Laboratory
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2. Outline and references
4/22/2017
Outline and references
Outline of this talk
Dual-sweep streak camera basics
Visualizing longitudinal (phase) motion
Visualizing transverse motion
Viewing the bunch closely: projection at an angle
Final remarks and summary
Past Papers / Reviews
Alex Lumpkin, “Advanced, time-resolved imaging techniques for electron-beam characterizations,” BIW 1990.
Ed Rossa, “Real time single shot three-dimensional measurement of picosecond photon bunches,” BIW 1994.
K.Scheidt, “Review of streak cameras for accelerators: features, applications and results,” EPAC 2000.
This is the outline of the talk.
After refreshing your memory about streak camera basics, I will show some examples of images showing time-sequence of events. In accelerator physics, this is called longitudinal motion. Next we will see how streak camera is used as fast movie camera taking film strips. Then we will take a look at the side views and top view examples.
Before finish, I will briefly comment on some design issues on optics transport.
Before I give my talk, I would like to point out that there are excellent reviews in the literature, some are in these workshops. Streak camera is a fairly common tool now, although still too expensive to be in every lab. All I will try to accomplish here is to show my particular way of telling the story and see whether you can be entertained.
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3. Streak camera basics: under the hood Cathode Ray Tube: Television
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Streak camera basics: under the hood Cathode Ray Tube: Television
Streak camera basics: under the hood Cathode Ray Tube: Z-axis Oscilloscope
Let us start from an instrument of entertainment: television tube.
In a TV tube , an electron beam is generated from the cathode, focused by electron optics onto the phosphor screen. A pair of deflection plate moves the focal spot vertically and another pair moves it horizontally.
Normally, two saw-tooth-shaped voltages are supplied to these deflection plates and the beam moves across the screen in a raster pattern. The horizontal scan is about 500 to 1000 times faster than the vertical scan.
A modulation on the grid voltage will cause an intensity change on the screen.
Hence it can display long time sequence. (an oscilloscope in Z-modulation mode)
The example shown here is the Morse code for B-I-W-0-6. The different length of the dashes and dots can be seen clearly. All code sequences are lined up except that for W, which is delayed from the periodic horizontal sync signal.
Next time you watch a television, thinks of it as a device that displays sequential signal in 2 dimensional space, folded.
The device has a fast time axis and slow time axis.
And it can be used to visualize pulse length and delay time of a quasi-periodic pulse train.
A device displaying a long sequential signal in a 2D space, folded
A fast time axis and a slow time axis
Visualize the length and phase of a quasi-periodic pulse train
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4. Use streak camera to visualize quasi-periodic light pulse train
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Streak camera basics: under the hood Principle of dual sweep streak camera
Use streak camera to visualize quasi-periodic light pulse train
Low optical magnification: the spot size has no consequences
Decide on two natural time scale of the dynamics being studied. Set scale of fast time axis (vertical) to match the shorter one, and that of the slow time axis (horizontal) to match the longer one
For very short time scales, use synchroscan: direct sine-wave drive
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5. 4/22/2017
Visualizing longitudinal motion Streak Image for Different APS Storage Ring Fill Patterns
T2 (1 ns range)
T2 (1 ns range)
T2 (1 ns range)
T1 (5 µs range)
24-singlets
T1 (5 µs range)
1+8*7
T1 (5 µs range)
324-singlets
User beam bunch timing at different fill patterns.
The vertical and fast time scale matches the bunch length
The horizontal and slow scale matches the circumference of the storage ring
24-singlets
Hybrid: 1+8*7
324-singlets
Bunch length (rms)
40 ps
Singlet (8 mA): 50 ps
Septuplet: 32 ps
25 ps
* Synchroscan streak camera was critical for reliable phase information
A.H. Lumpkin, F. Sakamoto, and B.X. Yang, Dual-sweep streak camera measurements of the APS user beams, PAC05.
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6. 4/22/2017
Visualizing longitudinal motion Longitudinal Instability at 200 mA Driven by an HOM
Normal user run 100 mA. Up to 250 mA in studies.
This is a longitudinal instability observed at 200 mA.
A high order harmonic of RF cavity drives the longitudinal instability
Each bunch oscillates at synchrotron frequency
Relative phase of the bunches are given by the 2pfHOM·nbucket·tRF
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7. 4/22/2017
Visualizing longitudinal motion ALS study of longitudinal beam dynamics at injection
J. M. Byrd and S. De Santis, “Longitudinal injection transients in an electron storage ring,” Phys. Rev. ST AB 4, (2001)
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8. 4/22/2017
Visualizing longitudinal motion APS Particle Accumulator Ring bunch compression
Left panel from C.Y. Yao, Harmonic Beam Capture Observation and Its Application to Harmonic RF Phase Control
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9. 4/22/2017
Visualizing longitudinal motion Storage Ring bunch compression via RF phase modulation
RF phase modulation induced beam shortening (Glenn Decker)
Every bunch for several micro-seconds
Low-cost approach to obtain compression ratio of 2
Glenn Decker et al. Transient Bunch Compression using Pulsed Phase Modulation in High-Energy Electron Storage Rings
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10. Visualizing Longitudinal Dynamics: Summary
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Visualizing Longitudinal Dynamics: Summary
Summary
Used as a very long-trace oscilloscope .
The smaller the light spot size, the better.
Match the fast and slow time scales to those of beam dynamics of interest.
Other techniques: Some measurements can be made by fast digital oscilloscopes as they become ever faster every year.
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11. Visualizing transverse dynamics A film strip of the front view
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Visualizing transverse dynamics A film strip of the front view
Fact: bunch length << bunch spacing in most accelerators
Increase optical magnification so we can see particle distribution
Slow down the fast scan speed so images of head and tail of the bunch overlap
Photo and copyright by Professor Andrew Davidhazy, Rochester Institute of Technology. Use with permission
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12. Kicker induced beam motion in the APS Storage Ring
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Visualizing transverse dynamics Film Strips of a Single Bunch / Multipass
Kicker induced beam motion in the APS Storage Ring
Vertical scale chosen to image betatron motion, horizontal and vertical
Horizontal scale chosen to visualize decoherence and emittance damping
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13. Visualizing transverse dynamics Transverse Multi-bunch Instabilities: short train
50 ms
(A) =0 (B) =0-3.0
(C) = (B) =0-5.2

14. Bursting mode instability
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Visualizing transverse dynamics Transverse Multi-bunch Instabilities: 324 Uniform Pattern
Bursting mode instability
Centroid oscillation in bursts. Not periodic.
Streak camera captures beam centroid motion and size changes
Work in progress
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15. Visualizing Transverse Dynamics: Summary
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Visualizing Transverse Dynamics: Summary
Summary for Framing Camera Mode
Need to select optical magnification so beam size or centroid motion can be measured. (Optical synchrotron radiation limited in spatial resolution!)
Match the fast and slow time scales to those of beam dynamics of interest.
Other techniques: Slower measurements, such as single-bunch single-turn imaging for a large accelerator, can be made by fast CMOS cameras.
Optical Magnification
Low
High
Scan Speed
Slow
(1) Longitudinal motion
(2) Transverse motion
Fast
(3) Bunch side/top views
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16. tan qy = Dy/Dz = yFS/ctFS Projection Tangent vs Aspect Ratio
Viewing the bunches in perspective Geometric Interpretation of Streak Images
sz = cst sy
Dz = cDt Dy qy
TV SCREEN
ELECTRON BUNCH
tan qy = Dy/Dz = yFS/ctFS
Projection Tangent
sy/sz
Aspect Ratio
Projection Tangent vs Aspect Ratio
Front-view: tan qy << sy/sz
Top-view: tan qy >> sy/sz
Side-view: tan qx >> sx/sz

17. High bunch current head-tail instabilities
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Viewing the bunches in perspective Top View Streak Image: Head-Tail Instability
High bunch current head-tail instabilities
High bunch current and low chromaticity
Synchrotron and betatron coupled excitation
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18. Viewing the bunches in perspective Synchro-betatron coupled motion - 1
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Viewing the bunches in perspective Synchro-betatron coupled motion - 1
Excited Head-Tail Oscillation
Synchro-betatron coupled motion excited by a transverse kicker
The motion has major contribution to decoherence of betatron motion
Proposal by Weiming Guo to generate ps x-ray pulse. To date, we have produced 6 ps photon bunch from 25 ps electron bunches.
Turn 195
Turn 0
HEAD
TAIL
Turn 30
Turn 60
Turn 80
Turn 120
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19. Viewing the bunches in perspective Synchro-betatron coupled motion - 2
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Viewing the bunches in perspective Synchro-betatron coupled motion - 2
HEAD
TAIL
TURN #123
HEAD
TAIL
TURN #153
TURN #112
At high bunch current, the vertical size increases faster after the kick. Decoherence is current dependent.
Is the claw-shaped bunch related to horizontal coupling? Three dimensional imaging should reveal the answer. (3D imaging, Edward Rossa, 1994)
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20. 4/22/2017
Viewing the bunches in perspective Imaging in the longitudinal phase space
On streak camera monitor, the location of an electron’s image point is given by
At a highly dispersive section, using a fast sweep, the energy and time terms dominate in the expressions, and we have an approximate longitudinal phase space map.
In linac, such map can be obtained at the spectrometer.
J. Rönsch, et al, “Longitudinal phase space studies at PITZ,” FEL’05, p 552.
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21. 4/22/2017
Visualizing longitudinal motion ALS study of longitudinal beam dynamics at injection
J. M. Byrd and S. De Santis, “Longitudinal injection transients in an electron storage ring,” Phys. Rev. ST AB 4, (2001)
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22. 4/22/2017
Viewing the bunches in perspective Imaging in the longitudinal phase space: ring
Off-phase injection of APS Booster (50 ms horizontal FS)
Off-phase injection of APS Booster (50 ms horizontal FS)
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23. Streak images: Longitudinal phase space damping
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Streak images: Longitudinal phase space damping
Off-phase injection of APS Booster showing phase space (50 ms horizontal FS)
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24. Viewing the bunches in perspective: Summary
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Viewing the bunches in perspective: Summary
Summary
Need to set optical magnification so the beam size can be measured.
Fast time scale always matches the bunch length.
Only slow time scales is adjustable for beam dynamics of interest. It sets a limit of several images per picture.
At locations of high dispersion, direct longitudinal phase space map can be taken.
Other techniques: More powerful (expensive) “streak cameras,” and only on linacs
Transverse deflection cavity + high-res OTR screens
Energy chirp using 0-phasing RF cavity + spectrometer
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25. Final remark on optics design issues Dispersion and bunch lengthening
4/22/2017
Final remark on optics design issues Dispersion and bunch lengthening
Converters
Optical synchrotron radiation: fast, limited spatial resolution
Optical transition radiation screens: fast, high spatial resolution
Cherenkov radiators: fast, high spatial resolution
Scintillators: fluorescence lifetime too long, good only for front view movies when bunch spacing is large.
Optics transport
Ideally all mirror optics transport. Dispersion of glass lengthens the light pulse. Narrow bandpass filter is necessary for ps-resolution.
Good spatial resolution requires large numerical aperture (optics acceptance angle). With large field of view, the optical transport has a minimum phase space requirement. It often determines a minimum diameter of the long transport pipe.
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26. Streak camera 101: Summary
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Streak camera 101: Summary
Summary
Streak camera has become standard imaging tools in the past two decades.
It is a flexible tool for visualizing beam dynamics in different time and spatial scales. Your need to
vary optical magnification to match the scale of the motion.
vary fast and slow time scales to match characteristic time of the dynamic phenomena.
Watching some of the pictures are entertaining.
Homework
Will you find a way to put it into everyone’s lab?
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27. Acknowledgment Acknowledgment SUPPORT AND ENCOURAGEMENT
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Acknowledgment
Acknowledgment
SUPPORT AND ENCOURAGEMENT
John Galayda, Glenn Decker, Om Singh
STUDIES
Alex Lumpkin, Louis Emery, Michael Borland,
Kathy Harkay, Weiming Guo, Yong-Chul Chae, C. Y. Yao
TECHNICAL SUPPORT
Frank Lenkszus, Bob Laird, Ned Arnold, Elbio Rotela,
Sushil Sharma, Joe Gagliano, George Goeppner
SPECIAL THANKS
Alex Lumpkin
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