X-ray Free-electron Lasers

Transcription

1 X-ray Free-electron Lasers Ultra-fast Dynamic Imaging of Matter II Ischia, Italy, 4/30-5/3/ 2009 Claudio Pellegrini UCLA Department of Physics and Astronomy

2 Outline 1. Present status of X-ray free-electron lasers (FELs). 2. Near future developments, using existing accelerator technology, electron/radiation pulses manipulation, HHG seeding, to produce: shorter pulses; improved longitudinal coherence; higher average brightness; wavelengths<0.1 nm; more compact, less costly FELs. 3 Further future developments, will use new electron sources, advanced laser-plasma accelerator, novel short period undulators for very compact, table-top FELs. 4 Conclusions. Ischia 5/1/2009 C. Pellegrini 2

3 Peak brightness of existing X-ray FELs, Flash and LCLS UCLA An old plot with superimposed FLASH and the very new LCLS data. Good predictions. Peak power in the 1-10 GW range. Ischia 5/1/2009 C. Pellegrini 3

4 LCLS first lasing at SLAC, April 2009, at 0.15 nm Courtesy LCLS group, SLAC Ischia 5/1/2009 C. Pellegrini 4

5 LCLS: FEL parameters Wavelength Å FEL parameter Cooperation length nm Peak saturation power 4 8 GW Average saturation power W Coherent photons/pulse Peak photon flux Ph/s Peak brightness* Average brightness* Instantaneous photon ΔE/E % Beam radius, rms µm Beam divergence, rms µrad Pulse duration, rms, fs *Ph./s/mm 2 /mrad 2 /.1%bw Ischia 5/1/2009 C. Pellegrini 5

6 LCLS: Other parameters Pulse repetition rate 120 Hz Single spike duration (0.15 nm) 1 fs Number of spikes 200 Spike line width 3x10-4 and, mostly important, more than10 9 photons per coherent volume (compare with less than 1 for spontaneous synchrotron radiation sources). This, and the FEL attribute of simultaneous short wavelength and short pulse length, nanometer to sub-nanometer, sub-picosecond to femtosecond, will lead us to explore a new range of phenomena. Ischia 5/1/2009 C. Pellegrini 6

7 Pulse trains of up to 800 µs duration Up to 10 Hz repetition rate (currently 5 Hz) Fixed gap undulators (Tune with electron beam energy) Wavelength range (fundamental): 6-47 nm Pulse energy average: 100 µj Peak power: ~ 5 GW Pulse duration (FWHM): fs Spectral width (FWHM): % Electron beam pulse train (30 bunches, 1 µs spacing, 5 Hz rep rate) Ischia 5/1/2009 C. Pellegrini 7 Courtesy Siegfried Schreiber, DESY

8 UCLA Transverse coherence at FLASH Double-slit diffraction pattern at 25.5 nm indicates good level of transverse coherence. (from XFEL TDR) Ischia 5/1/2009 C. Pellegrini 8

9 UV to X-ray FEL next developments Flash, LCLS, and the next FELs, like XFEL, SCSS, Fermi, are only the beginning of the road. Present and next generation FEL capabilities can be extended to these parameters: Photon energy, kev Pulse repetition rate, Hz Pulse duration, fs < Coherence, transverse Coherence length Peak Brightness Average brightness Polarization Very good L Bunch to L Cooperation ( µm) ph/mm 2 mrad 2 s 0.1%bw ph/mm 2 mrad 2 s 0.1%bw Variable, linear to circular Ischia 5/1/2009 C. Pellegrini 9

10 Two examples As an example of FELs development I will discuss two examples: Very short radiation pulses at about 1 and 0.15 nm High energy photon FELs, E>10keV Ischia 5/1/2009 C. Pellegrini 10

11 Example of developments: from 100fs to ultra-short X-ray pulses Many methods have been proposed to reduce the pulse length to the fs range: slotted spoiler; ESASE; two stage undulator with energy chirped pulse. All these methods select and use part of the electron bunch to lase. Pulse length can be as short as 1fs or less. The number of photons in the pulse is reduce by the number of electron lasing to the total number of electrons. There is a spontaneous radiation pedestal. Another possibility studied recently is to operate the FEL at low charge[1,2]. I use this case to illustrate what can be achieved. [1] Rosenzweig et al., Nuclear Instruments and Methods, A 593, (2008). [2] Reiche, Rosenzweig, Musumeci, Pellegrini, Nucl. Instr. And Methods, A 593, (2008). Ischia 5/1/2009 C. Pellegrini 11

12 Low charge electron bunches for ultra-short X-ray pulses Recent studies show that a smaller emittance (x 0.1), larger electron beam brightness (x ) and very short, ~ 1fs or less, electron bunches can be produced by reducing the bunch charge from about 1nC to few, 1 to 10 pc, and using velocity and magnetic bunching. SPARX: E=2 GeV, λ=3 nm, Single spike σ B =0.48 µm (1.6 fsec), 2x10 10 photons in the pulse. Ischia 5/1/2009 C. Pellegrini 12

13 LCLS 1pC example: attosecond pulses. UCLA λ = 0.15nm, σ E = 10 4, σ L = 160nm(530as). Beam current profile Peak power vs. z Single spike at saturation, with photons. Beam brightness~ 4x10 17 A/m 2 rad 2 compared to 6x10 15 A/m 2 rad 2 for the 1 nc design case. Ischia 5/1/2009 C. Pellegrini 13

14 LCLS at low charge, short pulses UCLA 20 pc λ = 0.15nm 20 pc λ = 1.5nm Y. Ding and the LCLS group, SLAC, and C. Pellegrini, UCLA, 2009 Part. Acc. Conf. Ischia 5/1/2009 C. Pellegrini 14

15 LCLS at low charge, short pulses Y. Ding and the LCLS group, SLAC, and C. Pellegrini, UCLA, 2009 Part. Acc. Conf. Ischia 5/1/2009 C. Pellegrini 15

16 60 KeV, short pulse FEL, using low emittance electron bunches The small emittance at 1pC can be used to obtain high energy photons at low beam energy with a short period undulator. Beam Parameters Energy =11.5 GeV I P =800 A ε N =6.x10-8 m σ E = 10-4 Undulator λ U =0.015 m K=1 FEL Parameters Wavelength 0.02 nm FEL parameter Gain Length 2.7 m Saturation power 1 GW Coherent Photons 10 8 Pulse length 0.5 fs Ischia 5/1/2009 C. Pellegrini 16

17 0.02nm, short pulse FEL UCLA Pulse duration~0.5 fs Power vs undulator length Spectrum Ischia 5/1/2009 C. Pellegrini 17

18 .. or a Compact soft X-ray FEL UCLA Beam energy 1.4 GeV S-band injector+x or C-band linac, length <35 m 1.5 cm period, K=1, undulator, length 15 m Bunch charge, 1-20 pc Pulse length, 1 to few fs Number of coherent photons/pulse, Linac repetition rate, 120 Hz X-ray Pulses in one linac pulse, 1 to 100 Synchronization to external laser using the signals from the photoinjector laser and the coherent radiation from the electron bunch after compression. Ischia 5/1/2009 C. Pellegrini 18

19 Optical manipulations techniques (1) UCLA ESASE Modulation Acceleration Bunching SASE Precise synchronization of x-ray output with the modulating laser Variable output pulse train duration Increased peak current and shorter x-ray undulator Solitary ~100-attosecond duration x-ray pulse A. Zholents, Phys. Rev. ST Accel. Beams 8, (2005) Peak current, I/I ka z /l L < fs section Ischia 5/1/2009 C. Pellegrini 19

20 Example with seed at 30 nm, radiating in the water window First stage amplifies low-power seed with optical klystron More initial bunching than could be practically achieved with a single modulator Output at 3.8 nm (8 th harmonic) 100 kw =30 nm 1 GeV beam 500 A 1.2 micron emittance 75 kev energy spread Optical manipulations techniques HHG LASER SEED Modulator =30 nm, L=1.8 m Modulator =30 nm, L=1.8 m Radiator =3.8 nm, L=12 m 300 MW output at 3.8 nm (8 th harmonic) from a 25 fs FWHM seed Ischia 5/1/2009 C. Pellegrini 20 Lambert et al., FEL04

21 Future developments II Plasma laser accelerators, 1 GeV/m or more, would greatly decrease the linac length. Novel electron sources, using plasmas or ultra-cold gases or.?., reducing the emittance below 0.1 mm mrad, and increasing the beam 6-D phase space density would give: Reduced beam energy for same wavelength Larger FEL parameter -> larger efficiency, photon number/electron, shorter pulse duration Undulators with small period, and large gap/period ratio, like microwave undulator or other new ideas, would also reduce the beam energy for the same wavelength. Ischia 5/1/2009 C. Pellegrini 21

22 Conclusions UCLA FLASH and LCLS are only the beginning of a new class of photon sources which will: Allow the exploration and manipulation of matter at the Angstrom-femtosecond level and the study of nonlinear phenomena Give fully longitudinal and transverse coherence Provide order of magnitudes larger peak and average brightness Reduce the cost and size of the sources while extending their performance Ischia 5/1/2009 C. Pellegrini 22