New Developments on Free Electron Lasers Based on Self-amplified Spontaneous Emission

1. New Developments on Free Electron LasersBased on Self-amplified Spontaneous Emission Why SASE FELs? How does it work? What are the challenges? Where are we? Where do we want to go? J. Rossbach, DESY J. Rossbach, DESY

2. Why SASE FELs? State of the art: Structure of biological macromolecule reconstructed from diffraction pattern of protein crystal: Needs 1015 samples Crystallized  not in life environment The crystal lattice imposes restrictions on molecular motion LYSOZYME , MW=19,806 Images courtesy Janos Hajdu J. Rossbach, DESY

3. Why SASE FELs? courtesy Janos Hajdu SINGLE MACROMOLECULE, Planarsection, simulated image Resol. does not depend on sample quality Needs very high radiation power @ 1Å Can see dynamics if pulse length < 100 fs J. Rossbach, DESY

4. Why SASE FELs? We need a radiation source with • ·    very high peak and average power • ·    wavelengths down to atomic scale λ ~ 1Å • ·    spacially coherent • ·    monochromatic • ·    fast tunability in wavelength & timing • ·    sub-picosecond pulse length For wavelengths below ~150 nm: SASE FELs. J. Rossbach, DESY

5. How does it work? Radiation power of oscillating point-like charge Q: P Q2 2 Q = Ne·e, Ne = # electrons Point charge radiates coherently P  Ne2! „Point“ means above all: bunch length < radiation Synchrotron radiation of an incoherent electron distribution:P  Ne Potential gain in powerNe = 109 – 1010 !! J. Rossbach, DESY

6. How does it work? Coherent motion is all we need !! J. Rossbach, DESY

7. How does it work? Idea:Start with an electron bunch much longer than the desired wavelength and find a mechanism that cuts the beam into equally spaced pieces automaticallyFree-Electron Laser (Motz 1950, Phillips ~1960, Madey 1970)Special version: starting from noise (no input needed)Single pass saturation ( no mirrors needed) Self-Amplified Spontaneous Emission (SASE)(Kondratenko, Saldin 1980)(Bonifacio, Pellegrini 1984) J. Rossbach, DESY

8. How does it work? Resonance wavelength: Spectrum of amplified spontaneous radiation J. Rossbach, DESY

9. How does it work? FIREFLY microbunching; Ricci,Smith/Stanford J. Rossbach, DESY

10. How does it work? 105 by FEL gain 103 by improved beam quality, long undulators J. Rossbach, DESY

11. What are the challenges? Overview Electron beam parameters needed forSelf-Amplified-Spontaneous Emission (SASE) Energy: für em= 1 Å: E  20 GeV Gain Length: Beam size: r  40 mhigh electron desity for maximuminteraction with radiation field Emittance  ≤  need special electron source to accelerate the beam before it explodes due to Coulomb forces Energy width: Narrow resonance E/E ≤ 10-4 Small distortion bywakefields  super conducting linac ideal! Peak current inside bunch: Î > 1 kA feasible only at ultrarelativistic energies, otherwise ruins emittance  bunch compressor Straight trajectory in undulator:ultimately < 10 m over 100 m J. Rossbach, DESY

12. Why a linear accelerator? X-ray SASE FEL needs: energy width σE/E ≤ 10-4 and bunch length σl 25 m (~100 fs)  σE  σl  60 eV m storage ring is limited to >1000 eV m electron emittance  ≤  10-11 m LEP (20GeV) (!): x > 10-10 m several kA peak current wakefields tolerable for single pass, BUT not in storage ring J. Rossbach, DESY

13. What are the challenges? RF gun TESLA FEL photoinjector for small and short electron bunches J. Rossbach, DESY

14. What are the challenges? Injector Layout of integrated injector/compressor for TTF2 and TESLA FEL J. Rossbach, DESY

15. What are the challenges? Bunch compression Beware of coherent synchrotron radiation (CSR) Magnetic bunch compression Beam dynamics simulation must take into account combined space charge and e.m. radiation in near-field. see: TRAFIC4 by A. Kabel/SLAC J. Rossbach, DESY

16. RF ‘streak’ 2.44 m V(t) sx e- sz D 90° bc bp y-z streak generated by deflector P. Emma, J. Frisch, P. Krejcik, G. Loew, X.-J. Wang What are the challenges? Bunch compression S-band Structures built at SLAC in 1960’s - now installed in linac for testing f = 2856 MHz V0 15 MV sz 22 mm P. Krejcik et. al., WPAH116 ‘slice’-e and ‘slice’ energy spread measurements also possible J. Rossbach, DESY

17. What are the challenges? Bunch compression Longitudinal electron bunch profile at the TESLA Test Facility measured with two different methods Interferometry of coherent synchrotron radiation Projection from longitudinal phase space tomography J. Rossbach, DESY

18. What are the challenges? Bunch compression Bunch compression down to few 20-30 m is a technical requirement (and complication) to achieve kA peak current for sufficiently small gain length. It is a lucky coincidence, that the ultra-short pulse length is exactly what users are calling for. From the user point of view, bunch length should be even  10 m !  try harder!  J. Rossbach, DESY

19. What are the challenges? Wakefields Smooth surface Wakefields from surface roughness: Test at TTF FEL E Rough surface, same diameter E See Markus Hüning, Wed. afternoon J. Rossbach, DESY

20. Where are we? Beam parameters In all key beam parameters, the extrapolation from proven technology is a factor 2 – 10 We know what to do and how We will take further steps at TTF getting even closer to TESLA FEL parameters J. Rossbach, DESY

21. Where are we?Progress with SASE FELs: VISA see: Tremain,Murokh WPPH118/122 Wed. afternoon J. Rossbach, DESY

22. Where are we?Progress with SASE FELs: LEUTL J. Rossbach, DESY

23. 530 nm Energy vs. Distance along the Undulator Exponential Growth Region Saturation of SASE Where are we?Progress with SASE FELs: LEUTL Flash of UV light (385 nm) near saturation. The expected wavelength as a function of angle (radial offset) is clearly seen. The darker “lines” are from shadows of secondary emission monitors in the vacuum chamber. Stephen Milton/ANL Tuesday 13:30h J. Rossbach, DESY

24. Where are we?Progress with SASE FELs: TESLA Phase 1 of the SASE FEL at the TESLA Test Facility at DESY, Hamburg. The total length is 100 m. J. Rossbach, DESY

25. Where are we?Progress with SASE FELs: TESLA TTF FEL undulator J. Rossbach, DESY

26. Where are we?Progress with SASE FELs: TESLA TTF FEL gain at 108 nm vs. bunch charge By now observed gain >105 SASE gain >1000 Spontaeous Emission x100 J. Rossbach, DESY

27. Where are we?Progress with SASE FELs: TESLA J. Rossbach, DESY

28. Where are we?Progress with SASE FELs: TESLA FEL wavelengths reached at TTF FEL J. Rossbach, DESY

29. Where are we?Progress with SASE FELs: Summary where wavelength year Livermore ~1 mm 1986 LURE/Orsay 5-10 m1997 UCLA/LANL 12 m 1998 LEUTL/Argonne 530 nm 1999 385 nm & saturation 2000 TTF FEL/DESY 80-180 nm 2000 VISA/BNL/LLNL/SLAC/UCLA 845 nm saturation 2001 (+2nd+3rd Harmon.) All observations agree with theoretical expectations/computer models J. Rossbach, DESY

30. Where do we want to go? SASE FEL projects under progress: min. wavelength APS/LEUTL Phase2 120 nm APS/LEUTL Phase3 51 nm DESY: TTF FEL Phase2 6 nm 2003/2004 SPring8: ~ 5 nm - 2005 SASE FEL projects proposed: SLAC: LCLS  0.15 nm 2006 DESY: TESLA XFEL  0.085 nm 2010 J. Rossbach, DESY

31. Where do we want to go? Brilliance Peak brilliance Average brilliance LCLS multibunch LEUTL TTF FEL J. Rossbach, DESY

32. Where do we want to go? LCLS J. Rossbach, DESY

33. Where do we want to go? LCLS Producing short bunches for LCLS 250 MeV z  0.19 mm   1.8 % 4.54 GeV z  0.022 mm   0.76 % 14.35 GeV z  0.022 mm   0.02 % 7 MeV z  0.83 mm   0.2 % 150 MeV z  0.83 mm   0.10 % Linac-X L0.6 m rf=180 RF gun Linac-1 L9 m rf -38° Linac-2 L330 m rf -43° Linac-3 L550 m rf -10° new Linac-0 L6 m undulator L120 m 21-1b 21-1d 21-3b 24-6d 25-1a 30-8c X ...existing linac BC-1 L6 m R56 -36 mm BC-2 L24 m R56 -22 mm DL-1 L12 m R56 0 DL-2 L66 m R56 = 0 SLAC linac tunnel undulator hall J. Rossbach, DESY

34. Short Bunch Generation in the SLAC Linac 50 ps RTL FFTB 9 ps 0.4 ps <100 fs SLAC Linac Add 12-meter chicane compressor in linac at 1/3-point (9 GeV) 1 GeV 20-50 GeV Existing bends compress to <100 fsec 30 kA 80 fsec FWHM 28 GeV ~1 Å Damping Ring (ge 30 mm) Compress to 80 fsec in 3 stages 1.5% New proposal for: • LCLS accelerator optics R&D • Ultra-short x-ray science program at SLAC P. Emma et. al., FPAH165 J. Rossbach, DESY

35. Where do we want to go? TESLA TESLA scheme J. Rossbach, DESY

36. Where do we want to go? TESLA Beam switchyard distributing the electron bunch trains to various undulators J. Rossbach, DESY

37. Where do we want to go? TESLA J. Rossbach, DESY

38. Where do we want to go? TESLA A potential site for TESLA near Hamburg J. Rossbach, DESY

39. Conclusion SASE FELs clearly demonstrated for wavelengths far below the visible. Full agreement with theory User facilities in the VUV/soft X-ray range just around the corner User facilities in the Angstrøm range are feasible with only moderate extrapolation of present state-of-the-art; Computer simulations and mechanical design are available Accelerator physics & technology will play major role Fun guaranteed! J. Rossbach, DESY