Kwang-Je Kim ANL & U of C& POSTECH Workshop on Sciences Outlook and R&D Issues of X-ray FEL Oscillator February 14-15, 2013 POSCO International Center Pohang, Korea Introduction to XFEL-O and Charges to the Workshop

2 Free Electron Laser Oscillator  A low-gain device with high Q optical cavity  Optical pulse formed over many electron passes  Difficult for x-rays –Electron beam qualities –High-reflectivity normal incidence mirror Science Outlook and R&D Issues for an XFELO Feb 14-15, 2013

Science Outlook and R&D Issues for an XFELO 3 X-Ray FEL Oscillator (XFEL-O)  An FEL oscillator is feasible in hard x-ray region by using Bragg mirrors –R. Collela and A. Luccio, 1983; KJK, Y. Shvyd’ko, and S. Reiche, 2008  Tuning is possible with a four mirror configuration –R. M.J.Cotterill, (1968) KJK & Y. Shvyd’ko (2009)  A super-conducting linac with a photo-cathode gun can drive an XFELO 3 Feb 14-15, 2013

Science Outlook and R&D Issues for an XFELO 4 Ginger Simulation of XFELO Spectrum After 500 Passes (Two Diamond Crystal Cavity, 50  m and 200  m, R. Lindberg) Feb 14-15, 2013

Temporal and spectral evolution of XFELO Science Outlook and R&D Issues for an XFELO 5 R.R. Lindberg, K.-J. Kim, Yu. Shvyd’ko, and W.M. Fawley, Phys. Rev. ST-AB. 14, (2011) Feb 14-15, 2013

An XFELO produces fully coherent, temporal as well as transverse, x-ray pulses Feb 14-15, 2013 Science Outlook and R&D Issues for an XFELO 6

7 Example Parameters  Electron beam: –Energy  6 GeV –Bunch charge ~ pC  low intensity –Bunch length (rms)  1 (0.1 ps)  Peak current 20 (100) A –Normalized rms emittance  0.2 (0.3) mm-mr, rms energy spread ~ 2  –Constant bunch rep ~1 MHz  Undulator: –L u = 60 (30) m,  u  2.0 cm, K=1.0 – 1.5  Optical cavity: –2- or 4- diamond crystals and focusing mirrors –Total round trip reflectivity > 85 (50) %  XFELO output: – 5 keV      25 keV –Bandwidth:  ~ 1 (5)  ; rms pulse length = 500 (80) fs –# photons/pulse ~ 1  10 9 –Rep rate ~ a few MHz 8 (..) indicates short-pulse mode for relaxed tolerances Feb 14-15, 2013

Science Outlook and R&D Issues for an XFELO 8 XFELO applications  High resolution spectroscopy –Inelastic x-ray scattering  Mössbauer spectroscopy –10 3 /pulse, 10 9 /sec Moessbauer  s (14.4 keV, 5 neV BW)  X-ray photoemission spectroscopy –Bulk-sensitive Fermi surface study with HX-TR-AR PES  X-ray imaging with nm resolution –Smaller focal spot with the absence of chromatic aberration  Other talks in this workshop Feb 14-15, 2013

An Ultimate X-Ray FEL Facility  A grand facility employing XFELOs and high-gain XFELs can be envisaged in which an XFELO serves as the seed for a high gain amplifier Feb 14-15, 2013 Science Outlook and R&D Issues for an XFELO 9

Accelerator Technology Issues  Basic configuration: low emittance gun + SCRF Linac  Gun –LCLS low charge operation demonstrated that the beam quality requirements for single pulse can be met –High rep rate (> MHz) guns have been constructed and are being tested  Cost saving R&D in super-conducting linac –High Q 0 (10 10  ) to save the refrigerator cost –Solid state RF power  One or more recirculation passes could reduce the cost –Use ERL but in accelerating phase Feb 14-15, 2013 Science Outlook and R&D Issues for an XFELO 10

Accelerator technology: Injector  DC gun for ERL(KEK/JAEA, Cornell) and the low frequency RF gun for NGLS will meet the XFELO requirements Feb 14-15, 2013 Science Outlook and R&D Issues for an XFELO 11 N. Nishimori, et al, WEPD51 C. Papadopoulus, et al., MOPD31

Feb 14-15, 2013 Science Outlook and R&D Issues for an XFELO 12

6 (7) GeV 3GeV ERL in the first stage XFEL-O in 2nd stage rf /2 path-length changer Using ERL loops for additional acceleration: KEK/JAEA project Feb 14-15, 2013 Science Outlook and R&D Issues for an XFELO 13

Challenges for X-ray Optical Elements  Diamond is best: high reflectivity and thermo- mechanical properties –Heat load dynamics: Can  E Bragg < 1 meV maintained? –Radiation damage issues  Stability of optical elements –Angular <10 nr & position< 3  1 kHz BW –Precision stages  Surface qualities –Reflectivity and wavefront distortion  Quality of grazing incidence focusing mirrors 14 Feb 14-15, 2013 Science Outlook and R&D Issues for an XFELO

Reflectivity of TISNCM* Diamond was measured to be >98% at the APS Science Outlook and R&D Issues for an XFELO 15 *Technological Institute for Superhard Novel Carbon Materials, Russia 16 Feb 14-15, 2013

Science Outlook and R&D Issues for an XFELO 16 Grazing Incidence, Curved Mirror  JTEC –Developing a technique combining elastic emission machining (slow) and electrolytic in-process dressing (fast) to fabricate a smooth surface to <nm height error and 0.25 mrad figure error –Issue: large difference in the sagital and meridional depths –Such mirrors are sought after by “every body” in SR business  Other ways of focusing –Curved crystal surface, CRL,.. H. Mimura, et. al. RSI 79, , 2008 Feb 14-15, 2013

Further opportunities for an XFELO: Extreme temporal coherence length from sub-mm  km  10 8 m(spontaneous emission limit)!  The XFEL-O output pulses are copies of the same circulating intra-cavity pulse  The pulse spacing needs to be stable to maintain a good overlap with electron beams:  T < 3  m  If the pulse spacing T can be controlled far more accurately,  T <0.01 /c, the spectrum of XFELO output becomes a comb  The extreme-stabilized XFEL-O may establish an x-ray- based length standard and have applications in fundamental physics—quantum gravity, wavefunction collapse of mesoscopic system Science Outlook and R&D Issues for an XFELO 17 Feb 14-15, 2013

Cavity stabilization by tying one of the comb lines to a nuclear resonance line (B.W. Adams and K.-J. Kim, to be published) Science Outlook and R&D Issues for an XFELO 18 Feb 14-15, 2013 Find the signal maximum by changing the cavity length ~1 Å and lock to it

Charge to Workshop  Identify the prospects and importance for sciences that can be done by XFELO  Are there scientific areas not discussed in this workshop? How can we find them?  Identify the technological challenges for constructing an XFELO, in accelerator and in x-ray optics.  Can the challenges be addressed by an R&D program, say, for 5 years?  Comment on the scientific prospects and technological challenges for an extreme-stabilized XFELO Feb 14-15, 2013 Science Outlook and R&D Issues for an XFELO 19