X-Ray Free Electron Lasers

1. X-Ray Free Electron Lasers Lecture 5. Self-amplified spontaneous emission. FLASH and the European XFEL in Hamburg Igor Zagorodnov DeutschesElektronen Synchrotron TU Darmstadt, Fachbereich 18 2. June 2014

2. Contents • Motivation • Shot noise in electron beam • Current modulation from shot noise • FEL start up from shot noise • Statistical properties of SASE radiation • FEL facilities • Outlook

3. Motivation How to obtain a useful external field? SASE Electrons produce spontaneous undulators radiation A. Kondratenko, E. Saldin, Part. Accelerators10, 207 (1980) R.Bonifacio et al, Opt. Comm.50, 373 (1984)

4. Motivation Low-energy undulator test line (LEUTL), USA 530 nm

5. Motivation TESLA Test Facility (TTF), Hamburg

6. Shot-noise in electron beam Fluctuations of the electron beam current density serve as the input signal in the SAS EFEL Laser pulse Spectrum

7. Shot-noise in electron beam The electron beam current (at the undulator entrance) consists from electrons randomly arriving at time tk The electron beam averaged over an ensemble of bunches The electron beam profile function can be, for example,

8. Shot-noise in electron beam In frequency domain It follows from central limit theorem that the real and imaginary parts are normally distributed The probability density distribution of spectral power

9. Shot-noise in electron beam First-order correlation function

10. Shot-noise in electron beam First-order correlation function Averaged spectral current density (“white noise”)

11. Current modulation from shot-noise We consider a rectangular averaged current

12. Current modulation from shot-noise Spectral power density of averaged current Parseval's theorem

13. Current modulation from shot-noise We are interested in an averaged spectral power density of shot noise, which by analogy can be written as The amplification takes place in bandwidth  and we can replace the power of the current in this bandwidth by power of the equivalent current with fluctuations at at amplitude

14. FEL start up from shot-noise High-gain FEL model with space-charge

15. FEL start up from shot-noise

16. FEL start up from shot-noise

17. FEL start up from shot-noise Start up from current modulation Start up from seed field

18. FEL start up from shot-noise On resonance energy

19. FEL start up from shot-noise Start up from seed field Start up from current modulation

20. FEL start up from shot-noise

21. Statistical properties of SASE radiation Interference Coherence Coherence is a property of waves that enables interference. Temporal coherence is the measure of correlation between the wave and itself delayed. it characterizes how well a wave can interfere with itself at a different time. The delay over which the phase or amplitude wanders by a significant amount is defined as the coherence time

22. Statistical properties of SASE radiation Coherence time The time-averaged intensity (blue) detected at the output of an interferometer plotted as a function of delay. The interference envelope gives the degree of coherence

23. Statistical properties of SASE radiation Coherence length Laserpuls Typical length of one spike Number of cooperative electrons Number of spikes (longitudinal modes)

24. Statistical properties of SASE radiation Spikes in spectrum Spectrum short bunch (~40fs) long bunch (~100fs) V. Ayvazyan et al, Eur. Phys.Journ. D 20, 149 (2002)

25. Statistical properties of SASE radiation Fluctuations of SASE pulse energy

26. Statistical properties of SASE radiation Fluctuations of SASE pulse energy (linear regime)

27. Statistical properties of SASE radiation Fluctuations of SASE pulse energy (after saturation, 13 nm, FLASH)

28. Statistical properties of SASE radiation Saturation length (SASE) SASE with electrons on coherence length

29. Statistical properties of SASE radiation Coherence Longitudinal profile with large statical fluctuations radiation electrons Transverse profile is coherent

30. FEL facilities TESLA Test Facility ( until 2002)

31. FEL facilities TESLA Test Facility ( until 2002) Three undulator modules. Total length 15m

32. FEL facilities TESLA Test Facility ( until 2002)

33. FEL facilities TESLA Test Facility ( until 2002)

34. FEL facilities TESLA Test Facility II ( 2002-2006) From 2003 on, TTF1 was expanded to TTF2, an FEL user facility for the spectral range of soft x-rays, including a new tunnel and a new experimental hall (in the foreground). In April 2006, the facility was renamed FLASH: FEL in Hamburg

35. FEL facilities FLASH ( from 2006)

36. FEL facilities FLASH ( from 2005)

37. FEL facilities FLASH ( from 2005)

38. Phase space linearization rollover compression vs. linearized compression Q=0.5 nC ~ 1.5 kA Q=1 nC ~2.5 kA

39. Phase space linearization FLASH In accelerator modules the energyof the electrons is increased from 5 MeV (gun) to 1200 MeV (undulator).

40. Phase space linearization FLASH In compressors the peak currentI is increased from 1.5-50 A (gun) to 2500 A (undulator).

41. Phase space linearization FLASH

42. FEL facilities FLASH 2 ( from 2013)

43. FEL facilities FLASH 2 ( from 2013)

44. FEL facilities FLASH 2

45. FEL facilities LCLS E= 3.5-14 GeV Intensity distrubution for λ= 0.14 nm radiation power ~ GW G.Gutt et al, PRL, 108, 024801 (2012) pulse length ~30 fs

46. FEL facilities LCLS P. Emma et al, Nature Photon. 4, 641(2010) λ=1.4 radiation power ~ GW Pulse length ~30 fs G.Gutt et al, PRL, 108, 024801 (2012)

47. FEL facilities European XFEL • kürzeste • Wellenlänge • größte • Brillanz

48. FEL facilities European XFEL

49. FEL facilities European XFEL

50. FEL facilities European XFEL