STREAK CAMERA 101 − Visualizing charged-particle beam dynamics 4/22/2017 STREAK CAMERA 101 − Visualizing charged-particle beam dynamics Beam Instrumentation Workshop – May 3, 2006 Bingxin Yang ASD/DIAG, Advanced Photon Source, Argonne National Laboratory Test

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. Test

Streak camera basics: under the hood Cathode Ray Tube: Television 4/22/2017 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 Test

Use streak camera to visualize quasi-periodic light pulse train 4/22/2017 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 Test

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. Test

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 Test

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, 024401(2001) Test

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 Test

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 Test

Visualizing Longitudinal Dynamics: Summary 4/22/2017 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. Test

Visualizing transverse dynamics A film strip of the front view 4/22/2017 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 Test

Kicker induced beam motion in the APS Storage Ring 4/22/2017 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 Test

Visualizing transverse dynamics Transverse Multi-bunch Instabilities: short train 50 ms (A) =0 (B) =0-3.0 (C) =0 -4.8 (B) =0-5.2

Bursting mode instability 4/22/2017 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 Test

Visualizing Transverse Dynamics: Summary 4/22/2017 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 Test

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

High bunch current head-tail instabilities 4/22/2017 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 Test

Viewing the bunches in perspective Synchro-betatron coupled motion - 1 4/22/2017 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 Test

Viewing the bunches in perspective Synchro-betatron coupled motion - 2 4/22/2017 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) Test

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. Test

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, 024401(2001) Test

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) Test

Streak images: Longitudinal phase space damping 4/22/2017 Streak images: Longitudinal phase space damping Off-phase injection of APS Booster showing phase space (50 ms horizontal FS) Test

Viewing the bunches in perspective: Summary 4/22/2017 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 Test

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. Test

Streak camera 101: Summary 4/22/2017 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? Test

Acknowledgment Acknowledgment SUPPORT AND ENCOURAGEMENT 4/22/2017 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 Test