X-ray FEL Oscillator (XFEL-O) Gun Requirements and R&D Overview FLS2010: WG5: High Brightness Guns March 1, 2010

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1 X-ray FEL Oscillator (XFEL-O) Gun Requirements and R&D Overview FLS2010: WG5: High Brightness Guns March 1, 2010 Nick Sereno (APS/ASD) - Argonne National Laboratory (ANL) / Advanced Photon source (APS) For the ANL XFEL-O Study Group M. Borland (ASD) B. Brajuskovic (AES) X. Dong (ASD) K-J Kim (ASD) (provided these slides) S. Kondrashev (PHY) R. Lindberg (ASD) B. Mustapha (PHY) A. Nassiri (ASD) P. Ostroumov (PHY) P. Piot (Northern Illinois University) Y. Shvyd'ko

2 Hard X-Ray FEL Oscillator Originally proposed in 1984 by Collela and Luccio and resurrected in 2008 (KJK, S. Reiche, Y. Shvyd ko, PRL 100, (2008)) Store an X-ray pulse from an undulator in a Bragg cavity X-ray pulse intensity exponentially increases toward saturation & is spectrally cleaned from Bragg reflections (MHz beam rep-rate) Bragg cavity provides very narrow ~2 mev X-ray bandwidth X-ray pulse evolves from incoherent to coherent pulse when (1+g)r >1 (g = single pass gain, r is total cavity reflectivity) Very challenging optical design and stabilization <~10 nrad crystal stabilization (LIGO technology) Promising experiment in APS S30. High average power incident on the crystals (must keep absorption losses low) 2

3 Tunable X-ray Cavity Two crystal scheme a very limited tuning (~7meV) Bragg angle must be kept small A tunable four crystal scheme Must provide a means of focussing the X-ray beam Tune cavity Bragg angle by adjusting S, F and G to keep round trip length constant de/e = 10-4 (1eV out of 10 kev), l cav ~200 m, ds ~ 20 mm, dg ~ 100 mm for a Bragg angle of 0.1 rad R. M.J.Cotterill, APL, 403,133 (1968) KJK & Y. Shvyd ko, PRSTAB (2009) 3

4 Tunable X-ray Cavity cont. Crystal choice Diamond Must be low Z for high reflectivity and normal incidence Highest reflectivity - R Dia = 5 kev, r = = 0.85 Best mechanical and thermal properties to handle high heat loads Use a thin crystal to outcouple the X-rays to the experiment T = 4%

5 Diamond backscattering : High reflectivity and narrow bandwidth Photon energy (kev) Courtesy of Yuri Shvyd ko 5

6 Ginger Simulation of XFELO Spectrum After 500 Passes (Two Diamond Crystal Cavity 50 mm and 200 mm R. Lindberg) KJK KEK Dec 21,

7 XFEL-O: Would deliver ultra-high spectral purity with high average power 7

8 XFELO Parameters Electron beam (Key Gun Parameters): Energy - 7 GeV Bunch charge ~ pc low intensity (g <~0.5 when r ~ 1) Bunch length (rms) 1 (0.1 ps) Peak current 20 (100) A Normalized rms emittance < 0.2 (0.3) mm-mr, energy spread (rms) ~ 2 x 10-4 Bunch rep ~1 MHz (driven by the Bragg cavity round trip time) (50 ma average current- JLAB recirculating linac) Undulator: L u = 60 (20) m, l u 2.0 cm, K = Optical cavity: 4- diamond crystals and focusing mirrors Total round trip reflectivity > 85 (50) % XFELO output: 5 kev 25 kev Bandwidth: dw/w ~ 1 (5) x 10-7, pulse length (rms) = 500 (80) fs # photons/pulse ~ 1x10 9 Harmonics feasible if x-ray pulse sees a crystal before grazing incidence mirror Blue color indicates short-pulse mode for relaxed tolerances 8

9 XFELO will revolutionize the hard x-ray techniques developed at storage-ring-based light sources and find new applications in areas complementary to SASE Inelastic x-ray scattering Mössbauer spectroscopy 10 3 /pulse, 10 9 /sec Mössbauer photons (14.4 kev, 5 nev BW) Bulk-sensitive Fermi surface study with HAXPES Time-resolved methods ( ps) X-ray imaging with near atomic resolution (~1 nm) Smaller focal spot with the absence of chromatic aberration X-ray photon correlation spectroscopy photons/sec is a game changer, better time structure than LCLS, t-coherence is a huge advantage Science/FEL WG ( Tu. 1:30-4:00 PM) 9

10 R&D Issues Towards an XFELO FEL beam dynamics, modeling R. Lindberg and W. Fawley (FEL WG Mon afternoon session) X-ray optics: crystals, stability Y. Shvyd ko (FEL WG, Mon afternoon session) Grazing incidence curved mirror A. Barty (FEL WG, Mon afternoon session) Injector A. Nassiri: ERL/HBEB, Tu. 4:30-4:55 PM N. Sereno: HBEB, Th. 9:00-9:30 AM Main accelerator A 7 GeV linac will be most versatile, accommodating other FELs ERL Option: R. Hajima, FEL/ERL WG, Th. 9:00-9:30 AM Recirculation: M. Borland, ERL/FEL WG, Th. 9:45-10:00 AM 10