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A MHz-repetition-rate hard X-ray free-electron laser driven by a superconducting linear accelerator

An Author Correction to this article was published on 27 July 2020

This article has been updated


The European XFEL is a hard X-ray free-electron laser (FEL) based on a high-electron-energy superconducting linear accelerator. The superconducting technology allows for the acceleration of many electron bunches within one radio-frequency pulse of the accelerating voltage and, in turn, for the generation of a large number of hard X-ray pulses. We report on the performance of the European XFEL accelerator with up to 5,000 electron bunches per second and demonstrating a full energy of 17.5 GeV. Feedback mechanisms enable stabilization of the electron beam delivery at the FEL undulator in space and time. The measured FEL gain curve at 9.3 keV is in good agreement with predictions for saturated FEL radiation. Hard X-ray lasing was achieved between 7 keV and 14 keV with pulse energies of up to 2.0 mJ. Using the high repetition rate, an FEL beam with 6 W average power was created.

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Fig. 1: Bird’s-eye view of the facility showing the location of the tunnel buildings in the urban area of the city of Hamburg.

European XFEL / Luftaufnahmen: FHH, Landesbetrieb Geoinf. und Vermessung

Fig. 2: View along the almost 1-km-long superconducting linac section L3, which accelerates the beam after the last bunch compression stage from 2.5GeV up to 17.5GeV.

DESY / Dirk Nölle

Fig. 3: Schematic layout of the European XFEL accelerator and photon beam transport.
Fig. 4: View of the undulator installation in the tunnel.

European XFEL / Heiner Müller-Elsner

Fig. 5: Integrated FEL pulse energy as a function of undulator magnetic length.
Fig. 6: SASE spectrum measured by the HiREX single-shot spectrometer.
Fig. 7: SASE FEL pulse energy measured for each X-ray pulse of a train of 500 bunches.

Data availability

The data that support the plots within this paper and other findings of this study are available from the corresponding author upon reasonable request.

Change history

  • 27 July 2020

    An amendment to this paper has been published and can be accessed via a link at the top of the paper.


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The accelerator of the European XFEL and major parts of the infrastructure have been contributed by the Accelerator Construction Consortium, coordinated by DESY. The consortium consists of Centre National de la Recherche Scientifique – Institut National de Physique Nucléaire et de Physique des Particules (CNRS–IN2P3, Orsay, France), Commissariat à l’Energie Atomique et aux Energies Alternatives – Institut de Recherche sur les Lois Fondamentales de l’Univers (CEA–IRFU, Saclay, France), DESY (Hamburg, Germany), Istituto Nazionale di Fisica Nucleare – Laboratori Acceleratori e Superconduttività Applicata (INFN–LASA, Milano, Italy), National Centre for Nuclear Research (NCBJ, Świerk, Poland), Wrocław University of Technology (WUT, Wrocław, Poland), The Henryk Niewodniczański Institute for Nuclear Physics – Polish Academy of Science (IFJ–PAN, Kraków, Poland), Institute for High Energy Physics (IHEP, Protvino, Russia), D.V. Efremov Scientific Research Institute of Electrophysical Apparatus (NIIEFA, St. Petersburg, Russia), Budker Institute of Nuclear Physics – Siberian Branch of Academy of Science (BINP, Novosibirsk, Russia), Institute for Nuclear Research – Russian Academy of Science (INR, Moscow, Russia), Centro de Investigaciones Energéticas, Medioambientales y Tecnológicas (CIEMAT, Madrid, Spain), Universidad Politécnica de Madrid (UPM, Madrid, Spain), Stockholm University (SU, Stockholm, Sweden), Uppsala University (UU, Uppsala, Sweden) and Paul Scherrer Institute (PSI, Villigen, Switzerland). A list of members of the Accelerator Construction Consortium is provided in the Supplementary Information.

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