STREAK CAMERA 101 − Visualizing charged-particle beam dynamics Bingxin Yang ASD/DIAG, Advanced Photon Source, Argonne National Laboratory Beam Instrumentation

STREAK CAMERA 101 − Visualizing charged-particle beam dynamics

Bingxin Yang

ASD/DIAG, Advanced Photon Source, Argonne National Laboratory

Beam Instrumentation Workshop – May 3, 2006

2Streak camera 101: Visualizing charged-particle beam dynamicsBeam Instrumentation Workshop, May 3, 2006

Bingxin [email protected]

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.



Streak camera basics: under the hoodCathode 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 hoodCathode Ray Tube: Television



Streak camera basics: under the hoodPrinciple 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 psSinglet (8 mA): 50 ps

Septuplet: 32 ps25 ps

T1 (5 µs range)

24-singlets

T1 (5 µs range)

1+8*7

T1 (5 µs range)

324-singlets

T2

(1

ns r

ange

)

T2

(1

ns r

ange

)

T2

(1

ns r

ange

)

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



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 2fHOM·nbucket·RF

1 ms

1 ns

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



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 dynamicsA 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 dynamicsFilm 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 dynamicsTransverse Multi-bunch Instabilities: short train

(A) =0 (B) =0-3.0

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

100 ns

50 s



Visualizing transverse dynamicsTransverse 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 SpeedSlow

(1) Longitudinal motion(2) Transverse motion

Fast (3) Bunch side/top views



Viewing the bunches in perspectiveGeometric 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/zAspect Ratio

z = ct

y

z = cty

y

tan y = y/z = yFS/ctFS

Projection Tangent

ELECTRON BUNCH TV SCREEN



Viewing the bunches in perspectiveTop 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 perspectiveSynchro-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 30Turn 0

HEADTAIL

Turn 120Turn 60 Turn 80

Turn 195



Viewing the bunches in perspectiveSynchro-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)

Kicker Off

Z (MM)

-40 -30 -20 -10 0 10 20 30 40

Y (

MM

)

0

2

4

6

8

10

12

14

16

18

Turn 125 (123 - 127)

Z (MM)

-40 -30 -20 -10 0 10 20 30 40

Y (

MM

)

0

2

4

6

8

10

12

14

16

18 HEADTAILTURN #123

Turn 110 (108 -112)

Z (MM)

-40 -30 -20 -10 0 10 20 30 40

Y (

MM

)

0

2

4

6

8

10

12

14

16

18

TURN #112

Turn 155 (153 - 157)

Z (MM)

-40 -30 -20 -10 0 10 20 30 40

Y (

MM

)

0

2

4

6

8

10

12

14

16

18 HEADTAILTURN #153



Viewing the bunches in perspectiveImaging 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

x x

streaky y v t

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 perspectiveImaging 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 issuesDispersion 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

AcknowledgmentSUPPORT 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

Documents

STREAK CAMERA 101 − Visualizing charged-particle beam dynamics Bingxin Yang ASD/DIAG, Advanced Photon Source, Argonne National Laboratory Beam Instrumentation