8th Call for Regular Proposals for User Experiments, call for Protein Crystal Screening Proposals and Expressions of Interest in Long-Term Proposals


The 8th call for regular proposals at European X-Ray Free-Electron Laser Facility (European XFEL) is open until Friday 03 December 2021 16:00 (local Hamburg/Schenefeld time – Central European Time CET) in User Portal to the European XFEL (UPEX) for all six scientific instruments currently in operation.

  • In the framework of this call, standard configurations for the FXE, MID and HED instruments can be specified in the UPEX proposal form.
  • A specific call for Protein Crystal Screening (PCS) proposals is also open at SPB/SFX in UPEX, with the same deadline as the regular call.
  • A call for expressions of interest in long-term proposals is also under way in the same time frame, information and electronic form are on a dedicated web page.

Refer to the complete announcement below for details and other important information for all applicants.

A virtual information meeting was held on 3 November 2021. Slides and a video of the presentations are available on the online event page.


Beamtime will be allocated to successful proposals from July to December 2022 at the following scientific instruments:

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

Please check with the relevant instrument group about specific feasibility conditions for this call before submitting a proposal. Please also inquire with the instrument groups 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.

1. Standard instrument configurations in this call

An efficiency advantage can be established on some instruments with the development of “standard configurations”. The goal is to allow user experiments to be grouped together back-to-back without involving a major change in setup every time. In addition, these standard configurations will help provide a pathway to broaden the user community by reducing the need for user teams to include the expertise needed to design/construct and install specific endstation components. A range of standard configurations may be offered by an instrument, alternating throughout a period that covers several calls, to limit the range of required setups on a temporary basis. A number of instruments will make available standard configurations in this call.

1.1 FXE: Chemistry chamber with liquid jet for simultaneous pump–probe, non-resonant XES and WAXS

We encourage users to submit proposals to use the liquid jet installation at FXE to perform non-resonant X-ray emission and scattering in parallel. This experiment station has been well established for measuring ultrafast dynamics of species in solution at repetition rates up to 500 kHz and time resolution of 100 fs. Typical measurements have often included X-ray emission of 3d metals, including simultaneous measurements of multiple lines. We anticipate successful proposals will be allocated between three to four 16-hour shifts. For proposals that may require parameters outside the ranges mentioned below, please contact the instrument group directly to clarify the specific details and determine your experiment’s compatibility with the standard configuration.

Optical laser parameters

Wavelength range 490–800 nm (TOPAS OPA)
800/400/267 nm (Harmonics)
Pulse duration < 60 fs
Typical pulse energies @ 1.1 MHz repetition rate >10 µJ for TOPAS OPA
>10 µJ for 267 nm,
40 µJ at 400 nm
>120 µJ at 800 nm
Higher pulse energies possible at 100 kHz laser operation
Focus size 100 µm
Polarization Linear (H, V) or circular


X-ray parameters

Incident X-ray energies 7, 9.3, or 12.5 keV
Repetition rate 100–500 kHz
Typical pulse energies >2 mJ
Focus size 10 µm
Polarization Linear horizontal


Experiment setup

Liquid jet diameter 100 µm
Sample volume >25 mL
Sample pump HPLC
Environment He atmosphere
Sample – scattering detector distance >10 cm
Demonstrated parallel X-ray emission measurements Cr K⍺ / Kβ / VtC
Fe K⍺ / Kβ
Co K⍺ / Kβ
Fe K⍺ and Co K⍺
Ni K⍺ / Kβ / VtC
Other configurations possible; please contact FXE for details.
Von Hamos Bragg angle range Vertical geometry 70–83°
Wide-angle scattering range 0.5 - 7 Å-1 (photon energy dependent)
Experimental geometry Quasi-collinear with incidence angle between the laser and X-ray beams: 15° or 3°, in horizontal plane.


1.2 HED standard configurations

1.2.1    Diamond Anvil Cell (DAC) standard configuration

  • IC2 standard DAC setup, symmetric DAC cell support for users who need cells, user-supplied BX90 with adapters
  • Optical observation microscope, streaked pyrometry for X-ray heating
  • 18 keV SASE, max. rep. rate of 4.5 MHz, >0.5 mJ pulse energy from the undulators (not accounting for beamline transmission)
  • 5–15 micrometer focal spot size (fixed at 5 µm, but effectively larger, depending on beam pointing stability)
  • Detectors: AGIPD mini-half detector and VAREX flatpanel
  • Required: Contact the HED instrument group for a feasibility check

1.2.2    ReLaX-SAXS-PCI standard configuration

  • IC1 chamber, 100 TW ReLaX laser incident on target at 45° w. r. t. XFEL (no normal incidence of laser on target)
  • SAXS+PCI @ 8.15 keV SASE (tunable within reasonable range), ca. 1 mJ per pulse, 2.25 MHz maximum rep. rate
  • +5–50 µm spot size (both X-ray and ReLaX), no nanofocus possibility
  • +PCI resolution of about 1µm
  • Backward HAPG X-ray spectrometer, forward spectrometer can be added only if SAXS diagnostics is not used
  • Laser diagnostics (upon request): EMP, electron, bremsstrahlung, and proton diagnostics
  • Further details: Contact the HED instrument group

1.3 MID – Small-angle MHz XPCS standard configuration

  • AGIPD MHz area detector, 1M pixels, 200 um pixel size
  • Photon energy: 7–12 keV, up to 2 mJ/pulse, up to 200 pulses/train, 10 trains/sec
  • Min. correlation function lag time 440 ns, max. lag time 88 µs
  • q-range (8 m sample–detector distance): ~7e-3 – 0.1 Ang-1 (small angle scattering)
  • Beam size on sample: 1–10 µm with local optics, >30 µm with tunnel optics
  • Standard mounts for sample in capillaries and scanning
  • Mounting of user-supplied sample environments possible (contact MID instrument group before proposal submission)
  • Further details: Contact the MID instrument group


2.         Protein Crystal Screening at SPB/SFX

Liquid jet injection is the most used sample delivery method for serial-femtosecond crystallography of proteins at the SPB/SFX instrument at the European XFEL. The complexity of sample preparation and injection may still lead to the loss of valuable beamtime during user experiments. In this call, our facility introduces a protein crystal screening (PCS) process that combines sample characterization and injection tests in the laboratories, followed by screening beamtimes at the SPB/SFX instrument. PCS proposals, submitted in a specific call in the user portal UPEX, will be selected after peer review and feasibility and safety checks.

This call exclusively covers injection by gas dynamic virtual nozzles (GDVNs) and double-flow focusing nozzles (DFFNs). Nozzles and injection support will be provided by the Sample Environment and Characterization (SEC) group. For further information, please contact Katerina Dörner (katerina.doerner@xfel.eu) prior to submission.


3.         Cross-instrument proposals

Highly targeted experiment proposals for a specific instrument have better chances of success. If, on the advice of our scientists, specific parts of your project should be conducted on different European XFEL instruments, 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. This option should not be used to submit the same experiment to two different instruments in order to increase the chances for beamtime allocation!


4.         X-ray beam conditions for the allocation period

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

Bunch duration [rms fs]

10–25 fs

Max. intra-train frequency [MHz]

4.5 MHz

Typ. number of pulses*




Photon energy range

Expected pulse energy range**


5–9.3 keV

2 mJ ± 20%

>9.3–14 keV

1 mJ ± 20%

>14–24 keV

0.5 mJ ± 20%


5.8–9.3 keV

2 mJ ± 20%

>9.3–12 keV

1 mJ ± 20%

>12–18 keV

0.5 mJ ± 20%




0.5–1.5 keV

5 mJ ± 20%

>1.5–2.5 keV

2 mJ ± 20%

>2.5 keV



* 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)

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


  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 two-colour w. variable delay (SA2; 6–10 keV; 0–0.5 ps)
    3. Soft X-ray two-colour w. variable delay (SA3; 500–3000 eV; 0–1 ps)
    4. Short bunches (< 10 fs); scheduling requires a sufficient number of experiments at several instruments; time-diagnostics is only partially available
    5. Full trains at instruments with << 10 Hz rep. rates (~ 2250 pulses)

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 the final schedule, continuous (24 hr) 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 corresponding instrument staff in order to clarify requirements.


5.         Experiment reports about previous beamtime

Experiment reports are mandatory and must be submitted 3 to 6 months after the end of each experiment. However, Main Proposers and/or Principal Investigators who have received beamtime in the past and who submit new proposals or continuation proposals must provide the experiment reports related to previous proposal(s) via the User Portal to the European XFEL (UPEX) by 6 December 2021. Missing experiment reports may result in withdrawal of new proposals from the review process. Please refer to further instructions on our homepage.


6.         Operation during COVID-19 pandemic

At present, it cannot be excluded that the travel restrictions that affected previous user runs and the specific hygiene measures applying to user operation at our facility this year will also influence operational aspects in the second part of 2022.

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

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


7.         Call for expressions of interest in long-term proposals

The European XFEL would like to assess the interest by the scientific community and the future impact of long-term proposals on our user access programme. Expressions of interest (EoI) in long-term research at our facility can be submitted until 3 December 2021. Please refer to the information and conditions on the specific EoI call page.


8.         User pages and funding options

More practical information for users can be found here:


Travel funding and living subsistence are available for a number of users affiliated with organizations based in the member countries of European XFEL. Further details are available here:


Specific shipping funding options for organizations based in the member countries of European XFEL are available in order to mitigate the impact of COVID-19 travel restrictions.


European XFEL User Office

Email: useroffice@xfel.eu

Phone: +49 (0)40 8998-6937 or -6767

  • 8th Call for Regular Proposals for User Experiments, call for Protein Crystal Screening Proposals and Expressions of Interest in Long-Term Proposals