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15th Call for Proposals for User Experiments

Time frame for the 15th Call for Proposals:

Allocation period 2027-I
Call opening week 14/2026
Call deadline Thursday, 07 May 2026, at 16:00 CEST (local Hamburg/ Schenefeld time/ Central European Summer Time)
Reports on previous experiments (see rules and who must provide reports by this deadline) 11 May 2026
PRP Meetings 09-10 July 2026
Feedback to proposers September 2026

15th Call for Proposals for User Experiments

 

The 15th call for proposals at the European X-Ray Free-Electron Laser Facility (European XFEL) is open until

Thursday, 07 May 2026, at 16:00 CEST
(local Hamburg/Schenefeld time / Central European Summer Time)


Please refer to the information below and apply via the User Portal to the European XFEL (UPEX). Beamtime will be allocated from March to July 2027 at these scientific instruments:

The next regular call for proposals is planned late 2026, for allocation in August to December 2027.

Before submitting a proposal, and for more information about user community projects, check with the relevant contacts about feasibility conditions:

 

In the framework of this call

  • In addition to regular proposals, the option of standard configurations for the HED and the MID instruments is available (see Section 1. below).
    The choice must be specified in the proposal form. At HED, priority access for the HIBEF User Consortium will reduce the available general user time by 30%. Questions on priority access should be directed to the HIBEF spokesperson, PD Dr. Toma Toncian (HZDR) (cf. HIBEF webpages).
  • In parallel, a call for proposals for members of the MHz XPCS Block Allocation Group (BAG) at MID is planned in the same time frame.
  • SCS: The instrument accepts proposals to XRD experiment station and hRIXS spectrometer. Details can be found in the fact sheet on the SCS instrument webpages.
  • SPB/SFX welcomes regular experiment proposals that can take advantage of the full capabilities of the instrument. In addition, an ongoing access scheme, QUick Access Screening Time (QUAST) is open for targeted screening and data completion at this instrument, in cooperation with the Sample Environment and Characterization (SEC) group. This access mode incorporates and extends the previously available protein crystal and sample screening. Please refer to the specific QUAST call information.

 

Specific requirements and technical feasibility of proposed experiments must be discussed with the relevant scientific instrument staff before proposal submission.

 

Proposals submitted in this call will be reviewed for their scientific quality by panels of international experts and checked for technical feasibility and safety 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. A number of instruments will make standard configurations available in this call.

1.1 HED standard configurations

HED users are always welcome to submit regular (non-standard platform) proposals that fit the instrument capabilities, according to the details given on the our HED-HIBEF website. However, before submission, it is mandatory to discuss your proposal with the instrument staff, as not all combinations of our capabilities are technically feasible.

 

Statement about alternating setups: DiPOLE XRD and DAC XRD proposals compete for the same resources, e.g. beamtime at 16.3 GeV electron energy and IC2 target chamber access. Therefore, European XFEL decided to schedule the DiPOLE XRD IC2 platform in each second half of a calendar year. Consequently, in this call for 2027-I, no standard DiPOLE IC2 XRD proposals will be accepted, in favour of DAC XRD proposals and minimum setup change-overs. We anticipate that in the next call 16 (opening in autumn 2026 for allocation in run 2027-II), no DAC XRD proposals will be accepted in favour of DiPOLE IC2 XRD proposals. Please note that this scheme does not apply to DiPOLE spectroscopy proposals at lower photon energies for IC1.

 

The following standard configurations will be available in the allocation period related to this call:

  • Two ReLaX standard configurations
  • Diamond Anvil Cell (DAC) standard configuration

Details: Conditions for the 15th call for proposals are on the HED web pages (https://www.xfel.eu/facility/instruments/hed/instrument_capabilities___call_for_proposals/index_eng.html)
The HED instrument group is available for questions and discussion of your project.

The following standard configuration is not available in this call and will be offered again in Call16, opening in autumn 2026 / allocation period 2027-II:

  • DiPOLE 100-X standard configuration

1.2 MID – Small-angle MHz XPCS standard configuration

In this call, regular experiment proposals to MID (refer to the conditions mentioned on the instrument webpages) are also welcome. Please discuss with the MID instrument scientists prior to submission.

In addition, this standard configuration is available:

  • AGIPD MHz area detector, 1 Mpx, 200 µm 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, >10 µm with tunnel optics
  • Standard mounts for sample in capillaries and scanning
  • Mounting of user-supplied sample environments possible (contact: mid-info@xfel.eu before proposal submission)
  • Further details: MID instrument group

2. Cross-instrument proposals

If, on the advice of our scientists, specific parts of your project should be conducted at different European XFEL instruments, the selection of two instruments is allowed in the proposal form, in order to submit a cross-instrument proposal. Please discuss with the respective instrument groups and make sure that the proposal and the experiment description addresses experiment sessions on both instruments exhaustively.
The cross-instrument proposal will receive individual IDs on submission to both instruments and will be reviewed by the relevant Proposal Review Panels. This option should not be used to submit the same experiment to two different instruments in order to increase the chances for beamtime allocation. Highly targeted experiment proposals for a specific instrument have better chances of success.

 

3. X-ray beam conditions for the allocation period

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

The provision of attosecond pulses at SASE2 and SASE3 is still under development and we therefore consider this a special mode. For specific parameters (photon energies, polarization states, purity, expected pulse durations), you need to inquire with the respective instruments.

 

Photon energy range

Expected pulse energy**

SASE1

5–9.3 keV

2 mJ

>9.3–14 keV

1 mJ

>14–24 keV

0.5 mJ

SASE2

5.8–9.3 keV

2 mJ

>9.3–12 keV

1 mJ

>12–24 keV

0.5 mJ

SASE3

0.4–1.5 keV

5 mJ

>1.5–2.5 keV

2 mJ

>2.5 keV

0.5 mJ

Bunch distribution: 350 X-ray pulses per instrument assume equal distribution at 2.25 MHz operation, with 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). Exact bunch distribution is based on needs of particular experiments and the capabilities of the photon delivery systems.

** Pulse energy depends on bunch charge, electron energy, and photon energy. The values in this table refer to average pulse energies in an optimized parameter setting. Depending on how much the actual parameters differ from these optimum values, the attainable pulse energies can be lower. It is very important to contact the instruments in order to evaluate the feasibility of your requirements

Explanations:

1. The above parameters correspond to the standard SASE operation mode. 

Starting with 2027-I, variable polarization (circular left/right; variable linear) is considered a standard operation mode at SASE3.

2. The following non-standard modes are available but may require more tuning and could be less reliable: 

a. Hard X-ray self-seeding (SASE2; 7–14 keV)

b. Hard X-ray two-colour with variable delay (SASE2; 6–10 keV; 0–0.5 ps) 

c. Soft X-ray two-colour with variable delay (SASE3; 400–3000 eV; 0–1 ps)

d. Short bunches (< 10 fs FWHM); requires coordinated scheduling as other instruments and available number of bunches might be affected; time-diagnostics is only partially available

e. Full trains at instruments with << 10 Hz rep. rates (~2250 pulses)

3. The following special modes are available but will likely require more tuning and may be less reliable. Interested PIs are strongly encouraged to contact the Leading Scientist of the respective instrument prior to proposal submission.

a. Attosecond pulse delivery at SASE3 (e.g. ≥200 as, few 100 µJ @ 1 keV)

Experiments requesting these non-standard and 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 h) 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.

 

4. 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 Monday, 11 May 2026, in some cases even earlier than the typical timeline of 3-6 months. Missing experiment reports may result in withdrawal of new proposals from the review process. Please refer to the complete information on this web page:
https://www.xfel.eu/users/user_guide/experiment_report

 

5. Information for users and funding options

Practical information for users (e.g. about travel funding) can be found here: https://www.xfel.eu/users
 

General enquiries can be directed to the European XFEL User Office

Email: useroffice@xfel.eu

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

 

Before submitting a proposal, always discuss with the relevant instrument group about specific feasibility conditions
 

  • 15th Call for Proposals for User Experiments

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