Author: Faatz, B.
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TUP2WA03 Harmonic Lasing in X-Ray FELs: Theory and Experiment 68
  • E. Schneidmiller, B. Faatz, M. Kuhlmann, J. Rönsch-Schulenburg, S. Schreiber, M. Tischer, M.V. Yurkov
    DESY, Hamburg, Germany
  Harmonic lasing in XFELs is an opportunity to extend operating range of existing and planned X-ray FEL user facilities*. Contrary to nonlinear harmonic generation, harmonic lasing can provide much more intense, stable, and narrow-band FEL beam which is easier to handle due to the suppressed fundamental. Another interesting application of harmonic lasing is Harmonic Lasing Self-Seeded (HLSS) FEL*,** that allows to improve longitudinal coherence and spectral power of a SASE FEL. Recently*** this concept was successfully tested at FLASH2 in the range 4.5 - 15 nm. That was also the first experimental demonstration of harmonic lasing in a high-gain FEL and at a short wavelength (before it worked only in infrared FEL oscillators). In this contribution we describe the concepts of harmonic lasing and of HLSS FEL, and present the experimental results from FLASH2.
* E.Schneidmiller and M.Yurkov, Phys. Rev. ST-AB 15(2012)080702
** E.Schneidmiller and M.Yurkov, Proc. of FEL2013, p.700
*** E.Schneidmiller et al., Phys. Rev. Accel. Beams 20(2017)020705
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Optimizing of Electron Beam Distribution at European XFEL and FLASH  
  • B. Faatz
    DESY, Hamburg, Germany
  As a rule, FELs have been single user machines. To distribute the electron beam with a fast kicker system between different undulators enables delivering beam to several users simultaneously. If it is done from RF pulse to RF pulse, it would decrease the number of bunches for each user. Therefore, it is planned at the European XFEL and already practice for several years at FLASH, to kick entire bunch trains within an RF pulse, thus delivering to both users the 10 Hz trains. It will be shown how the system has allowed long pulse trains for two users simultaneously and what has been done to keep the full flexibility within a bunch train not only in terms of wavelength, number of bunches and bunch separation, but also in bunch length needed to allow different users different FEL-pulse duration.  
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