1. A U.S. Department of Energy Office of Science Laboratory Operated by The University of Chicago Argonne National Laboratory Office of Science U.S. Department of Energy Generating Picosecond X-ray Pulse at APS Through Beam Manipulation Weiming Guo Accelerator Physics Group / ASD Advanced Photon Source

2. 1 Pioneering Science and Technology Office of Science U.S. Department of Energy Acknowledgements Michael Borland Katherine Harkay Vadim Sajaev Chunxi Wang Bingxin Yang

3. 1 Pioneering Science and Technology Office of Science U.S. Department of Energy Outline Brief review of short pulse generation methods. Introduce idea of synchrobetatron coupling method. Linear synchrobetatron coupling and decoherence beam dynamics. Experimental results. Conclusions.

4. 1 Pioneering Science and Technology Office of Science U.S. Department of Energy Longitudinal Phase Space Manipulation Methods I tt    = 0.096%   t = 20 ps 1.Lower  c 2.Increase s : 2 nd rf system, lower energy 3. Voltage modulation

5. 1 Pioneering Science and Technology Office of Science U.S. Department of Energy Longitudinal Phase Space Manipulation Methods II tt  dipole D(s) Lower  c Voltage modulation V rf = V 0 (1+  cos m  0 t)sin h  0 t m ~2 s 0

6. 1 Pioneering Science and Technology Office of Science U.S. Department of Energy Tilt the Bunch to Get Shorter Pulses Shorter Pulse y z Initial bunch Tilted bunchPhotonsSlit  z  = 5.8mm,20ps  l  =  y /   y =8  m,0.03ps Shorter Pulse

7. 1 Pioneering Science and Technology Office of Science U.S. Department of Energy Physics Limits Voltage modulation * ~ 2 10 Nonlinearity Increase s, s →0.5 ~60 0.3 cavity number Low  c,f s →1/  E ** ~65 0.3  c,n, x-z coupling Vertical tilt *** ~660 0.03 Physical aper. Method Maximum Pulse lengthLimitation Comp. ratio (ps) * Glenn Decker ** Vadim Sajaev *** Michael Borland

8. 1 Pioneering Science and Technology Office of Science U.S. Department of Energy Deflecting Cavity and Synchrobetatron coupling z y y y′y′y′y′ y y′y′ y A(z) sin( x  +  ) Betatron Osci. Cavity Kick ‹y› (z): Slice centroid ‹y 2 › (z): Slice beam height ‹y›: Bunch centroid ‹y 2 ›: Bunch height Magnet Kick Synchrobetatron Coupling A sin( x  +  (z) ) y′y′ y

9. 1 Pioneering Science and Technology Office of Science U.S. Department of Energy Particle Motion After A Vertical Kick y y′y′ Before the Kick After Betatron Oscillation y y′y′

10. 1 Pioneering Science and Technology Office of Science U.S. Department of Energy Tune Difference by Momentum Spread      HeadTail Vertical tune The phase advance due to chromaticity is Longitudinal motion

11. 1 Pioneering Science and Technology Office of Science U.S. Department of Energy Phase Difference by Momentum Spread Vertical tune The phase advance in half synchrotron period Betatron Oscillation Average in one Slice

12. 1 Pioneering Science and Technology Office of Science U.S. Department of Energy 4 D Phase Space Simulation Longitudinal phase space: Transverse phase space: Synchrobetatron coupling: Initial distribution: Gaussian in both planes Note: simplified simulation, nonlinearity and damping not included.

13. 1 Pioneering Science and Technology Office of Science U.S. Department of Energy Simulation Result Bunch shape after ½ synchrotron period Centroid oscillation

14. 1 Pioneering Science and Technology Office of Science U.S. Department of Energy Decoherence Concept If all particles have same oscillation frequency and phase, motion is coherent. If the oscillation phase is uniformly distributed, the ensemble average is constant, and the particle motion is incoherent. The progression from coherent motion to incoherent motion is called decoherence. In accelerators decoherence is usually caused by tune spread, and is accompanied by emittance increase.

15. 1 Pioneering Science and Technology Office of Science U.S. Department of Energy Decoherence by Quantum Excitation I Simulation by Elegant Quantum excitation effect

16. 1 Pioneering Science and Technology Office of Science U.S. Department of Energy Decoherence by Quantum Excitation II Longitudinal map

17. 1 Pioneering Science and Technology Office of Science U.S. Department of Energy BPM Signal V=4kV, I=1.3mA, Cy=2.4, Cx=2.6, s =0.0078 X-y coupling The modulation frequency Fast decoherence; persistent motion in damping time scale. The decoherence stops with modulation y x Turn

18. 1 Pioneering Science and Technology Office of Science U.S. Department of Energy BPM Signal Envelop Fit V=4kV, I=1.3mA, Cy=3.5, s =0.0078, m =0.0035. We believe the amplitude tune dependence is small; it has the same feature as quantum excitation decoherence; we hope for one slice under low current, small kick, quantum excitation decoherence dominates.

19. 1 Pioneering Science and Technology Office of Science U.S. Department of Energy Experiment Setups for Streak Camera Imaging C y was lowered to 4, C x =6 was unchanged. We were able to store 1.3 mA current. The kicker strength applied to the beam was 4kV, or, 0.12 mr, which corresponds to 0.5 mm in the straight sections. The kicker frequency is 2 Hz. The streak camera was set up to take images turn by turn, in (y,z) plane. Resolution: Y 0.43 ps(0.13mm), Z 2.2 ps. Images were taken from 0 to 190 turns after the kick, from which we found the best turn to obtain shorter pulses. The effective slit width was 100  m.

20. 1 Pioneering Science and Technology Office of Science U.S. Department of Energy Streak Camera Measurement Results Turn 83-87 Gaussian fit of one slice Pixel size: 0.036mm*1.2ps

21. 1 Pioneering Science and Technology Office of Science U.S. Department of Energy Streak Camera Measurement Results The emittance of the center slice The center tilt angle

22. 1 Pioneering Science and Technology Office of Science U.S. Department of Energy Shorter Pulse The current was only 0.2 mA per bunch. The profile is the overlap of 10 consecutive bunches. The bunch length was 31 ps. Streak camera resolution and optical effects are not subtracted. Turn number Longitudinal position Kicker strength longitudinal tune Minimum achievable pulse length

23. 1 Pioneering Science and Technology Office of Science U.S. Department of Energy Conclusion Linear synchrobetatron motion Decoherence caused by quantum excitation BPM and streak camera data Effective and convenient Shortest pulse 3 ps

24. 1 Pioneering Science and Technology Office of Science U.S. Department of Energy BPM signal fit