Lessons from the LEUTL Zone

1. Lessons from the LEUTL Zone Stephen Milton and John Lewellen (plus a cast of others) Argonne National Laboratory Injector Commissioning Workshop, SLAC 11 October 2006

2. The APS SASE-FEL

3. Overall Philosophy • Do FEL Experiment • No New Technology that is not Absolutely Necessary

4. Undulator Line

5. Undulator Line Diagnostics

6. Undulator Line Diagnostics

7. 7 . 1 10 6 . 1 10 5 . 1 10 4 . 1 10 3 . 1 10 Intensity [arb. units] 100 10 1 0.1 0.01 0 5 10 15 20 25 Distance [m] Optical Intensity Gain 530nm 10 March 01 dataset DS1

8. 7 . 1 10 6 . 1 10 5 . 1 10 4 . 1 10 3 . 1 10 Optical Intensity Statistics 0.75 Unsaturated Intensity [arb. units] Norm. Std. Dev. Intensity 100 Saturated 10 1 0.1 0.25 0.01 0 5 10 15 20 25 Distance [m]

9. Second Harmonic Gain

10. VLD2 (4.8 m) VLD7 (16.8 m) VLD9 (21.6 m) VLD3 (7.2 m) VLD5 (12 m) Z-Dependent SASE Spectra – 385 nm Simulation Experiment VLD2 (4.8 m) Simulation VLD3 (7.2 m) VLD5 (12 m) VLD7 (16.8 m) VLD9 (21.6 m)

11. 6 10 5 10 4 10 3 10 Microbunching Measurement SASE light Intensity [arb. units] CTR light 100 10 1 0.1 0 5 10 15 20 25 Distance [m]

12. Simultaneous Spectra: Fundamental and 2nd Harmonic

13. Optical Pulse Characterization

14. Wavelength Tunability(Saturation Achieved) 110 nm? 130 nm 220 nm 385 nm 530 nm 540 nm 660 nm Wavelength [nm]

15. LEUTL Basic Layout

16. Linac Details Spectrometer L3 Chicane L1 L2 Spectrometer Spectrometer L4 L5 Booster Bypass PAR Bypass Und. 1 Und. N Spectrometer

17. Photocathode RF GunDrive Laser - Basic Specifications

18. LEUTL Drive Laser Room

19. Other Features of Laser • Basics • 6 Hz • No Longitudinal Shaping • Iris used for transverse shaping • Features • Remote control of all significant tuning and steering • Added Locally • Virtual Cathode • Additional Diagnostics • Insertable screens • Energy Meters • One in tunnel did not always work • Every measurement that one can make without changing anything should be available in the control room

20. Laser Problems • Stability • Mostly Energy • Wandering Arrival Phase • Day-to-day transverse uniformity • Better at lower power • Required for better stability • On all the time • But burnt out flashlamps more often • Replace flashlamps every maintenance period • Pulse Selection from Regen • Double pulses • Basically required • A laser expert • Two-year learning period • Reasonable expectations

21. Photocathode RF GunCavity - Basic Specifications

22. PC Gun and First Section

23. PC Gun Problems • Cathode Quality • QE • Uniformity • Strong impact on emittance • Both changed over time • Basic Cathode Design • Difficult to tune • Difficult to seal • Stability Required • Power on gun 24/7 • Gun beat up after a few years of ops • Probably impact tune of gun • Not enough diagnostics on gun • Zero mode effects • Not careful enough at restoring absolute launch times • Solenoid • Unwanted quadrupole term • Made matching difficult

24. 31 Oct 01 – before 1st cleaning 5 Nov 2001 - after 1st cleaning 4 Dec 2001 - after 1st cleaning 10 Dec 2001 - after 2nd cleaning Cathode Issues ?

25. “Normal” Performance

26. Switching to LEUTL Operations • Shut down rf, modulators ready-to-pulse • Reconfigure rf waveguide switch • Standardize / degauss all linac magnets • Switch linac timing source to 11.9 MHz master clock (for trigger sync.) • Bring rf systems back up • Bring magnets back up

27. LEUTL Operational Issues • Single shift operation • Required restarting each shift (every 8 or 12 hours) • Impacted everything • Gun • Laser • Bunch compression • Linac Match • Lesson • A machine the works great for 3rd generation operations is no where near good enough for 4th generation ops

28. Beam Property MeasurementTwiss Parameters and Matching Matching Section 3 YAG screens in free-space drift region APS LINAC Given Obtain Profile measurements Distance between screens Beam parameters a, b, e Beamline geometry Quad settings Settings for “perfect” match into LEUTL line

29. Twiss Parameters and Matching Beam Property Measurement PAR Bypass 3-screen region 4.8 m 4.8 m

30. Notes on Matching and Beam Transport • Matching • Two 3-screen Locations • One following the bunch compressor • One following the linac • Algorithm used not especially robust • Two “others” (Quad Scans) • After 1st linac section • Near undulator • Not very effective or used regularly • Should have had another 3 screen system in front of undulator • Matching Difficult at best • Highly dependent on • initial transverse distribution • Charge • Laser pulse length • Steering for wakefields • Not preserved day to day

31. More Notes on Transport • Wakefields • Near the gun at low energy • Mirror • 1st accelerating structure • Along the length of the undulator • Beam Position Monitors • Bunch Length/pattern Effects • Single bunch vs. bunch trains • Compressed vs. not Compressed

32. Notes About the Bunch Compressor • Moveable Magnets • Transverse • Longitudinal • Configured for better study of CSR • Diagnostics • Full suite • Except no local bunch length monitor • Bunch length measurement • Linac zero-phasing technique • Simple and Effective (100 fs resolution)

33. Bunch Compressor

34. Bunch Compressor

35. Bunch Length Beam Property Measurement linac section run at zero-crossing 4 - 7 ps

36. Bunch Compressor Studies

37. What We Would Do Differently if We Were able to Do it Again • Condition • Given the initial infrastructure we had • Teach scuba instead • Laser • Diode pumped laser • Oblique laser injection • Gets rid of wakes from mirror • Frees up beamline for other diagnostics • Cathode • Metal? • Think about CsTe and removable cartridge (loadlock) • Issues with field • Some other materials

38. What We Would Do Differently if We Were able to Do it Again • RF Gun • Add more diagnostics • New gun style • New solenoid style • Linac • Add more diagnostics with better resolution • General House keeping • Operations • Remove 7 GeV Beam dump system • Improves availability of linac for FEL work

39. Acknowledgements and Thanks N.D. Arnold, C. Benson, W. Berg, S.G. Biedron, M. Borland, Y.-C. Chae, R.J. Dejus, P.K. Den Hartog, B. Deriy, M. Erdmann, Y.I. Eidelman, E. Gluskin, M.W. Hahne, Z. Huang, K.-J. Kim, Y. Li, A.H. Lumpkin, O. Makarov, S.V. Milton, E.R. Moog, A. Nassiri, V. Sajaev, R. Soliday, N. Sereno, B.J. Tieman, E.M. Trakhtenberg, G. Travish, I.B. Vasserman, N.A. Vinokurov, G. Wiemerslage, B.X. Yang Friends and Colleagues V. Bharadwaj, D. Dowell, P. Emma, J. Galayda, W. Gei, B. Faatz, W. Fawley, H. Freund, J. Power, X.J. Wang,….

41. Thank You