Author: Saldin, E.
Paper Title Page
MOP008 Theoretical Computation of the Polarization Characteristics of an X-Ray Free-Electron Laser with Planar Undulator 38
 
  • G. Geloni
    XFEL. EU, Hamburg, Germany
  • V. Kocharyan, E. Saldin
    DESY, Hamburg, Germany
 
  We show that radiation pulses from an X-ray Free-Electron Laser (XFEL) with a planar undulator, which are mainly polarized in the horizontal direction, exhibit a suppression of the vertical polarization component of the power at least by a factor λw2/(4 pi Lg)2, where λw is the length of the undulator period and Lg is the FEL field gain length. We illustrate this fact by examining the XFEL operation under the steady state assumption. In our calculations we considered only resonance terms: in fact, non resonance terms are suppressed by a factor λw3/(4 pi Lg)3 and can be neglected. While finding a situation for making quantitative comparison between analytical and experimental results may not be straightforward, the qualitative aspects of the suppression of the vertical polarization rate at XFELs should be easy to observe. We remark that our exact results can potentially be useful to developers of new generation FEL codes for cross-checking their results.  
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MOP085 Scheme to Increase the Output Average Spectral Flux of the European XFEL at 14.4 keV 251
 
  • V. Kocharyan, E. Saldin
    DESY, Hamburg, Germany
  • G. Geloni
    XFEL. EU, Hamburg, Germany
 
  Inelastic X-ray scattering and nuclear resonance scattering are limited by the photon flux available at SR sources, up to 1010 ph/s/meV at 14.4 keV. A thousand-fold increase may be obtained by exploiting high repetition rate self-seeded pulses at the European XFEL. We report on a feasibility study for an optimized configuration of the SASE2 beamline combining self-seeding and undulator tapering at 14.4 keV. One should perform monochromatization at 7.2 keV by self-seeding, and amplify the seed in the first part of the output undulator. Before saturation, the electron beam is considerably bunched at the 2nd harmonic. A second part of the output undulator tuned to 14.4 keV can thus be used to obtain saturation at this energy. One can further prolong the exchange of energy between the photon and the electron beam by tapering the last part of the output undulator. Start-to-end simulations demonstrate that self-seeding, combined with undulator tapering, allows one to achieve more than a hundred-fold increase in average spectral flux compared with the nominal SASE regime at saturation, resulting in a spectral flux of order 1013 ph/s/meV. A more detailed description of this study can be found in*.
* G. Geloni, V. Kocharyan and E.~Saldin, "Scheme to increase the output average spectral flux of the European XFEL at 14.4 keV", DESY 15-141 (2015).
 
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MOP086 Novel Opportunities for Sub-meV Inelastic X-Ray Scattering Experiments at High-Repetition Rate Self-seeded XFELs 257
 
  • O.V. Chubar
    BNL, Upton, Long Island, New York, USA
  • G. Geloni, A. Madsen
    XFEL. EU, Hamburg, Germany
  • V. Kocharyan, E. Saldin, S. Serkez
    DESY, Hamburg, Germany
  • Yu. Shvyd'ko
    ANL, Argonne, Ilinois, USA
  • J. Sutter
    DLS, Oxfordshire, United Kingdom
 
  Inelastic x-ray scattering (IXS) is an important tool for studies of equilibrium dynamics in condensed matter. A new spectrometer recently proposed for ultra-high-resolution IXS (UHRIX) has achieved 0.6 meV and 0.25/nm spectral and momentum Transfer resolutions, respectively*. However, further improvements down to 0.1 meV and 0.02/nm are required to close the gap in energy-momentum space between high and low frequency probes. We Show that this goal can be achieved by further improvements in x-ray optics and by increasing the spectral flux of the incident x-ray pulses. UHRIX performs best at energies from 5 to 10 keV, where a combination of self-seeding and undulator tapering at the SASE2 beamline of the European XFEL promises up to a hundred-fold increase in average spectral flux compared to nominal SASE pulses at saturation, or three orders of magnitude more than possible with storage-ring based radiation sources. Wave-optics propagation shows that about 7·1012 ph/s in a 90-microeV bandwidth can be achieved on the sample. This will provide unique new possibilities for IXS. Extended information about our work can be found in**.
* Y. Shvyd'ko et al., Nature Communications 5:4219 (2014).
** O. Chubar et al., ‘Novel opportunities for sub-meV inelastic X-ray scattering at high-repetition rate self-seeded X-ray free-electron lasers', http://arxiv.org/abs/1508.02632, DESY 15-140, (2015).
 
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