# Presentation: 050661

## STREAK CAMERA 101    − Visualizing charged-particle beam dynamics

*Bingxin Yang*
*ASD/DIAG, Advanced Photon Source, Argonne National Laboratory*

**Beam Instrumentation Workshop – May 3, 2006**

## 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.

**Notes:**
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.

## Streak camera basics: under the hoodCathode Ray Tube: Z-axis Oscilloscope

- 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

- Streak camera basics: under the hood***Cathode Ray Tube: Television***

**Notes:**
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.  

## 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

## Visualizing longitudinal motion Streak Image for Different APS Storage Ring Fill Patterns

|  | 24-singlets | Hybrid: 1+8*7 | 324-singlets |
| --- | --- | --- | --- |
| Bunch length (rms) | 40 ps | Singlet (8 mA): 50 ps
Septuplet: 32 ps | 25 ps |

- T1  (5 μs range)
- 24-singlets

- T1  (5 μs range)
- 1+8*7

- T1 (5 μs range)
- 324-singlets

- T2   (1 ns  range)

- T2   (1 ns  range)

- T2   (1 ns  range)

- A.H. Lumpkin, F. Sakamoto, and B.X. Yang, Dual-sweep streak camera measurements of the APS user beams, PAC05.

- * Synchroscan streak camera was critical for reliable phase information

**Notes:**
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

## 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 2fHOM·nbucket·RF 

- Each bunch oscillates at synchrotron frequency
- Relative phase of the bunches are given by the 2***f**HOM**·**n**bucket**·****RF*

- Visualizing longitudinal motion*** ******Longitudinal Instability at 200 mA Driven by an HOM***

**Notes:**
Normal user run 100 mA. Up to 250 mA in studies.
This is a longitudinal instability observed at 200 mA. 

## 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**, 024401(2001)

## 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

## 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

## 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.

## 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

## 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

## Visualizing transverse dynamicsTransverse Multi-bunch Instabilities: short train

- (A) =0			 (B) =0-3.0

- (C) =0	-4.8	                 (B) =0-5.2

## 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*

## 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 |

## Viewing the bunches in perspectiveGeometric Interpretation of Streak Images

**Projection Tangent vs Aspect Ratio**
**Front-view**: tan *y* << *y*/*z*
**Top-view**: tan *y* >> *y*/*z*
**Side-view**: tan *x* >> *x*/*z*

*******y*****/*********z***
**Aspect Ratio**

**tan ********y**** = *********y*****/*********z***** = *****y*****FS****/*****ct*****FS**
**Projection Tangent**

**ELECTRON BUNCH**

**TV SCREEN**

## 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

## 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.

## Viewing the bunches in perspectiveSynchro-betatron coupled motion - 2

- 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)

## Viewing the bunches in perspectiveImaging in the longitudinal phase space

- J. Rönsch, et al, “Longitudinal phase space studies at PITZ,” FEL’05, p 552.

- 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.

## 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**, 024401(2001)

## Viewing the bunches in perspectiveImaging in the longitudinal phase space: ring

- Off-phase injection of APS Booster (50 s horizontal FS)

- Off-phase injection of APS Booster (50 ms horizontal FS)

## Streak images: Longitudinal phase space damping

- Off-phase injection of APS Booster showing phase space (50 s horizontal FS)

## 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

## 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.

## 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?

## 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