7th Call for Proposals for User Experiments at the European XFEL

The European X-Ray Free-Electron Laser Facility (European XFEL) encourages the scientific community worldwide to submit proposals for User Experiments via the User Portal to the European XFEL (UPEX) until Wednesday 16 December 2020 16:00 (local Hamburg/Schenefeld time – Central European Time CET)

(Note the unusual deadline time!)

A virtual information meeting on this call for proposals was held on 25 November 2020. Details about the videoconference are available here:



Beamtime will be allocated to successful proposals from July to December 2021 at the following scientific instruments:

  • Through a separate process, SCS is currently organizing specific User-Assisted hRIXS Commissioning projects. Information on this additional opportunity is available on our user pages

Instrument overview: https://www.xfel.eu/facility/instruments


Please check with the relevant instrument team about specific feasibility conditions for this call before submitting a proposal. Please also inquire with the instrument teams for more information about planned user community projects:


All proposals submitted in this call will be reviewed for their scientific quality by panels of international experts and checked for safety and feasibility conditions.

The conditions expected for this allocation period are listed below. Nevertheless case-by-case verification about specific feasibility conditions with the instrument teams is required.


7th EuXFEL Call for Proposals

(Allocation: July– December 2021)





Photon energy [keV]*

5 – 24

0.5 – 3.0

Max. mean pulse energy **[mJ]

0.5 – 4

1 – 10

Bunch duration [rms fs]

10 – 25

10 – 25

Max. intra-train frequency [MHz]



Typ. number of pulses***




* Safety restrictions currently apply for photon energies below 5.8 keV. To remove these is work in progress.

** Pulse energy depends on bunch charge, electron energy and photon energy. 

*** Bunch distribution: 400 X-ray pulses per instrument assume equal distribution at 2.25 MHz operation.Higher or smaller numbers for higher/smaller intra-train frequency. Max. 2250 electron bunches within 500 µs are available for distribution to the instruments (4.5 MHz) once safety restrictions are lifted.



  1. The above parameters correspond to the standard SASE operation mode.
  2. The following Special modes are available, but require more tuning and are less reliable:
    1. Hard X-ray Self-Seeding (SA2; 7 - 14 keV);
    2. Hard X-ray 2-color w. variable delay (SA2; 6 – 10 keV; 0 –  0.5 ps) and
    3. Soft X-ray 2-color w. variable delay (SA3; 500 – 3000 eV; 0 – 1 ps).
    4. Short bunches (< 10 fs) in reduced charge mode of the accelerator. Scheduling requires a sufficient number of experiments at several instruments. Time-diagnostics is only partially available.

Experiments requesting these special modes should address the development of new techniques and fields and are expected to involve large communities and facility staff. If included in final schedule, continuous (24 hrs) beam delivery would be planned in this case. Since there is a vast range of detailed specifications for these special modes, proposers are requested to contact the respective instrument staff in order to clarify requirements.

Operation during COVID-19 pandemic

At present it cannot be excluded that the travel restrictions which affected part of 2020 and the specific hygiene measures applying to user operation at our facility this year will also influence operational aspects in the second part of 2021.

In run 202002 it was aimed at keeping the lowest number of users on site as possible. ‘Remote’ user access for all experiments was encouraged and considered as the general rule.

In the proposal form you are requested to detail to which degree your proposal would be affected by the persistence of pandemic conditions and which measures could be taken in order to mitigate these consequences, still preserving good chances of success.

In case of doubt, please contact the instrument teams for advice.


Cross-instrument proposals

Highly targeted experiment proposals for a specific instrument have better chances of success. If, on advice of our scientists, specific parts of your project should be conducted on different EuXFEL instruments, now the selection of two instruments is possible in the proposal form. Make sure that the proposal addresses the experiment sessions on both instruments exhaustively. For schedule reasons, the proposal will receive individual IDs on submission and will be reviewed by both instrument proposal review panels concerned.


User pages

More practical information for users can be found here.


User funding options

  • Travel funding and living subsistence is available for a specified number of users affiliated with organizations based in the member countries of European XFEL. Further details are available here.
  • Also for this call, limited travel funding for users from organizations in non-member countries is also available through the EU support programme CALIPSOplus. The offer applies to experiments completed by 31 October 2021.
  • Specific shipping funding options for organizations based in the member countries of the European XFEL could be made available in order to mitigate the impact of COVID19 travel restrictions.