Author: Lutman, A.A.
Paper Title Page
TUOAI02
 Hard X-ray Self-Seeding at the LCLS  
 
  • R.R. Lindberg, W. Berg, D. Shu, Yu. Shvyd'ko, S. Stoupin, E. Trakhtenberg, A. Zholents
    ANL, Argonne, USA
  • J.W. Amann, F.-J. Decker, Y.T. Ding, Y. Feng, J.C. Frisch, D. Fritz, J.B. Hastings, Z. Huang, J. Krzywinski, H. Loos, A.A. Lutman, H.-D. Nuhn, D.F. Ratner, J.A. Rzepiela, D.R. Walz, J.J. Welch, J. Wu, D. Zhu
    SLAC, Menlo Park, California, USA
  • V.D. Blank, S. Terentiev
    TISNCM, Troitsk, Russia
  • P. Emma
    LBNL, Berkeley, California, USA
  • S. Spampinati
    Elettra-Sincrotrone Trieste S.C.p.A., Basovizza, Italy
  
  Funding: U.S. Dept. of Energy Office of Sciences under Contract No. DE-AC02-06CH11357
The Linac Coherent Light Source (LCLS) has produced extremely bright hard x-ray pulses using self-amplified spontaneous emission (SASE) since 2009. In SASE, the electron beam shot noise initiates the FEL gain, resulting in output radiation characterized by poor temporal coherence and a fluctuating spectrum whose normalized width is given by the FEL bandwidth. Recently, colleagues at DESY suggested a self-seeding scheme for the LCLS to reduce the bandwidth*. Here, the SASE produced in the first half of the undulator line is put through a simple diamond-based monochromator; the resulting monochromatic light trailing the main SASE pulse is used to seed the FEL interaction in the downstream undulators. We report on the experimental results implementing such a scheme at the LCLS, in which we have measured a reduction in bandwidth by a factor of 40-50 from that of SASE at 8-9 keV. The self-seeded FEL operates close to saturation, with the maximum output energy approximately equal to that with no seeding for low charge. The observed level of power fluctuations in the seeded output is presently rather large, and future plans focus on discovering their origins and reducing their magnitude.
* Geloni, V. Kocharyan ,and E.L. Saldin, DESY 10-133, arXiv:1008.3036 (2010)
 		 
slides icon Slides TUOAI02 [22.104 MB]  
 
TUOB04 Comparison of Hard X-Ray Self-seeding with SASE after a Monochromator at LCLS 217
 
  • J.J. Welch, F.-J. Decker, J.B. Hastings, Z. Huang, A.A. Lutman, M. Messerschmidt, J.L. Turner
    SLAC, Menlo Park, California, USA
  
  Funding: ** Work supported in part by the DOE Contract DE-AC02-76SF00515.
Self-seeding of a hard x-ray FEL was demonstrated at LCLS in January 2012 and produced a factor of 40-50 bandwidth reduction using a electron bunch charge of 20-40 pC*. For many hard x-ray users, the photon intensity after a monochromator is an important performance parameter. In this paper, we report results from a subsequent study of self-seeding performance using the Si (111) K-monochromator with a full bandwidth of 1.2 eV at 8.2 keV. These include a direct comparison of the average intensity of the monochromatized seeded beam with that of a monochromatized fully tuned-up SASE beam, in both cases using 150 pC bunch charge. The intensity distribution, fluctuations, and spatial profiles of the monochromatized radiation are studied and compared.
* J. Amann, et. al, Nature Photonics, to be published 		 
slides icon Slides TUOB04 [1.417 MB]  
 
THPD56 Two-color FEL Generation based on Emittance-spoiler Technique 654
 
  • C. Feng, Y.T. Ding, Z. Huang, J. Krzywinski, A.A. Lutman
    SLAC, Menlo Park, California, USA
  
  Generation of two-pulse two-color x-ray radiation is attracting much attention within the free-electron laser (FEL) user community. Femtosecond x-ray pulses with variable durations and separation can be simply generated by the emittance-spoiler foil method* at the Linac Coherent Light Source (LCLS). In this paper, we describe three FEL schemes rely on the emittance-spoiler technique for the generation of two intense x-ray pulses with different colors. With a representative realistic set of parameters of LCLS, numerical simulations confirm that two femtosecond x-ray pulses at ten gigawatt level with different wavelengths around 1.8 nm can be generated by these schemes. The central wavelengths of the output pulses can be easily altered by changing strengths of the undulators.
*P. Emma et al., PRL 92, 074801 (2004).