LCLS Run 26 Call for Proposals

LCLS Call for Proposals for period: March 2026 – July 2026 (Run 26)

Submission Deadline: 06 August 2025 (4:00 PM Pacific Time)

We are pleased to announce the call for LCLS Proposals for Run 26. This Run will offer capabilities on the soft and hard X-ray instruments using the LCLS normal conducting (NC) accelerator at 120 Hz while the superconducting accelerator is undergoing a major upgrade to higher energies under the LCLS-II-HE project. While undergoing this upgrade, both the soft and hard X-ray undulators will be operated up to 120 Hz. Three soft X-ray instruments will be available for user proposals (TMO, chemRIXS and qRIXS). For the hard X-ray instruments, vertically polarized 5 to 25 keV X-rays in the fundamental will be available, as well as rapid tuning / scanning capability using the variable gap system for both undulators. The hard X-ray undulator will provide beam to the suite of hard X-ray instruments (XPP, XCS, MFX, CXI & MEC). In Run 26, the XPP instrument will return to operations after an upgrade to be ready for the upcoming LCLS-II-HE capabilities. XPP will be able to operate with the copper beam at 120 Hz during this Run.

User proposals are sought for all X-ray instruments, as described below.

Please contact LCLS Instrument Scientists to discuss instrument options for your proposal. For new users this is especially important to help ensure your proposal is as competitive as possible.

Register and submit your proposals through the Universal Proposal System (UPS). 

For further information about this system please visit the link below:

Universal Proposal System Information

A Virtual LCLS “Town Hall” User Meeting to discuss Run 26 will be held at 9:00 am Pacific Daylight Time on July 16, 2025.

Virtual "Town Hall" Meeting Information

User proposals for the soft X-ray instruments (TMO, chemRIXS and qRIXS) using LCLS-II 120 Hz beam.

TMO:

The Time-resolved Atomic, Molecular and Optical Science instrument (TMO) was developed to study the dynamics of isolated quantum systems using charged particle spectroscopy, pump/probe methodologies, and/or nonlinear X-ray interactions. The TMO instrument will continue to be available for User experiments in Run 26 and will perform experiments using the normal conducting accelerator with a maximum repetition rate of 120 Hz. There will be three standard configurations offered at the first interaction point (IP1): the magnetic bottle electron time-of-flight spectrometer (MBES), the energy- and angle- resolving electron spectrometer (MRCO), and the co-axial velocity map imaging (cVMI) instrument. All configurations make use of the OPCPA laser system which can be operated at 120 Hz. We specifically encourage the submission of proposals making use of the XLEAP sub-fs pulse capabilities.

For more information please check our website and/or contact Instrument Lead James Cryan (jcryan@slac.stanford.edu) with any questions.

chemRIXS:

ChemRIXS is a dedicated instrument to study condensed phase chemistry with pump-probe spectroscopy. For Run 26 chemRIXS will be available for general user proposals using a maximum of 120 Hz repetition rate from the LCLS normal conducting accelerator. The liquid standard configuration of chemRIXS is optimized for pump-probe experiments using liquid jets. We specifically encourage the submission of proposals making use of the XLEAP sub-fs pulse capabilities. A new Fresnel zone plate based photon spectrometer downstream of the chemRIXS interaction point will be available for these experiments. Additionally, the OPCPA laser system with 800 nm fundamental wavelength, harmonics, and an OPA is available. The new high-throughput SVLS spectrometer with nominal 2000 resolving power will be available for PFY-XAS measurements. Simultaneously with the spectrometer, upgraded detectors for transmission-XAS and APDs for total fluorescence yield XAS detection will be offered.

For more information please check our website and/or contact Instrument Lead Kristjan Kunnus (kristjan@slac.stanford.edu) with any questions.

qRIXS:

qRIXS is a dedicated instrument designed to investigate correlated-electron condensed matter systems using a wide variety of time-resolved spectroscopy methods.  It will be made available for general user proposals in the Run 26 call for proposals at 120 Hz repetition rate. The qRIXS instrument supports a wide variety of experimental techniques, such as time-resolved resonant inelastic x-ray scattering, transient X-ray absorption, diffraction, and reflectivity.  In general, due to the 120 Hz repetition rate, time-resolved RIXS will not be offered, unless an exceptionally strong case is made with supporting evidence for technical viability.  Optical excitation from THz to UV is provided by the Carbide laser system, driven at the fundamental wavelength of 1030nm.

For more information please check our website and/or contact Instrument Lead Georgi Dakovski (dakovski@slac.stanford.edu) with any questions.

User proposals for the Hard X-ray Instruments using the 120 Hz accelerator 

The hard X-ray instruments of LCLS (XPP, XCS, MFX, CXI & MEC) will be available using the 120 Hz accelerator as in previous LCLS runs.

Proposals that make use of the Standard Configurations available on each of the Hard X-ray Instruments are highly encouraged, including short proposals that can make use of a more limited amount of beamtime with higher likelihood of scientific success using those standard configurations.

Proposals for XCS, MFX and CXI will make use of the same capabilities as for prior Runs, with details to be found on the LCLS website. For XPP and MEC there are some important new aspects, as detailed below:

XPP:

XPP will restart user operations after a period of re-commissioning in Run 26. XPP will re-establish Standard Configuration capabilities: such as time resolved in-air diffraction, low temperature environment and versatile laser parameters. XPP will also support X-ray only experiments using the “mini-split and delay” system. Details are found at the XPP Instrument website.

One major change for XPP and the LCLS facility is the method used to multiplex the hard-X-ray beam. The previous multiplexing scheme was based on a thin crystal to let most of the beam pass through while selecting a small bandwidth for XPP. Such a scheme is not compatible with LCLS-II-HE and therefore a new multiplexing approach based on using the zeroth and first order of gratings will now be employed. This results in a reduction of the expected pulse intensity for multiplexed monochromatic experiments at XPP, with ~20% of the pulse energy compared with the previous multiplexing approach. The new multiplexing scheme uses the 1st order diffraction of a transmission grating and a reflection from Si(111). The previous multiplexing method used a thin Diamond (111) monochromator.

XPP experiments can happen with 3 beam configurations:

  1. Using the standard grating to deliver 10% of the pink beam from the source then monochromatized with Si(111). This will be favored by the facility to enable multiplexed experiments.
  2. Using the second grating to deliver 25% of the pink beam from the source then monochromatized with Si(111). A strong justification will be required for proposals needing to use this grating as it reduces the beam performance for the other multiplexed experiment.
  3. No grating using the full LCLS pink beam (no multiplexing) can be available with a strong scientific justification of the need.

LCLS seeks proposals that allow multiplexing as this supports a great number of experiments. The new multiplexing mode allows for multiplexed experiments using self-seeding.. LCLS encourages proposals that can make use of a multiplexed self-seeded beam.

For more information please check our website and/or contact Instrument Lead Takahiro Sato (takahiro@slac.stanford.edu)

MEC:

Proposals in the area of Matter in Extreme Conditions (MEC) are welcomed in all relevant areas of science, as usual, and for any instrument. As in the prior call, there is particular focus on the area of Inertial Fusion Energy (IFE):

IFE Science: Proposals that address IFE Priority Research Opportunities (PROs) are sought, with one key example being studies that address IFE wetted foam target physics. There is a goal of scheduling 50% of MEC science experiments in the IFE area, consistent with strategic priorities from DOE. Such proposals should be clearly indicated as addressing IFE and reference the relevant PRO numbers within the proposal. Select MEC  as a review panel for your proposal and answer “Yes” to the question “Should the proposal be evaluated as IFE priority research?”. Then select the relevant PRO numbers from the list below during the proposal submission process. These proposals will be reviewed by a sub-panel of experts in IFE science, alongside a sub-panel for general MEC science.

For a detailed description of the PROs, see the 2022 IFE Basic Research Needs (BRN) Workshop Report.

For more information on any aspect of MEC, please contact Instrument Lead Eric Galtier (egaltier@slac.stanford.edu) with any questions.

LCLS Hard X-ray Instrument Contacts:

 

Proposal Types Available (for all instruments)

LCLS Proposal Preparation Guidelines

(1) General User Proposals

A Proposal Template has been created to provide guidance on the format and structure of submissions. Users are strongly encouraged to follow this guidance, to help ensure that appropriate information is supplied to the Proposal Review Panel (PRP). This template along with updated proposal preparation guidelines will also be discussed during the Virtual Town Hall on July 16, 2025.

Proposals that can be scientifically successful using fewer than the typical 5 shifts are strongly encouraged if the scientific needs are consistent with a shorter duration. Proposers are asked to make it clear in their proposals that level of risk and scientific ambition is consistent with the number of shifts requested. See also the DC&S proposal option below.

Standard Configurations:

For Run 26, LCLS will continue to emphasize the use of Standard Configurations, where a target of 50% or more of the beamtime is expected to be awarded to experiments utilizing the many configurations available. These provide a defined platform for running many similar experiments efficiently, leading to more users and experiments being allocated beam time. Proposals that make use of the Standard Configurations available are highly encouraged, including shorter experiments that can make use of a more limited amount of beamtime with higher likelihood of scientific success using a standard configuration.

Standard Configurations proposals require the inclusion of a parameter table, which can be found on the instrument-specific website. Users are strongly encouraged to contact the relevant instrument scientists to discuss and plan their proposals of any kind, but especially those that use (or could be adapted to use) Standard Configurations.

(2) Dataset Collection and Screening (DC&S) proposals:

LCLS offers a short proposal mechanism for experiments that can make use of a short amount of beamtime (one or two shifts) using a frequently deployed configuration to collect or complete a dataset, or screen samples in preparation for a regular LCLS proposal. DC&S proposals need to make use of a configuration already in place for regular LCLS experiments and they are therefore scheduled “as opportunity arises”. This access mechanism is tailored to:

  • Experiments where one or two shifts would be sufficient to complete an existing or collect a full dataset, suitable for publication. As part of the proposal, your science case should justify why your experiment can be accomplished in 1 - 2 shifts. If applicable, it should reference the previously reviewed proposal or beamtime.
  • New user groups or projects that need half a shift (6 hours) to gain experience or screen samples in preparation for submitting a full proposal.

Note that the DC&S proposal mechanism unifies and replaces the Protein Crystal Screening (PCS) and Data Set Collection (DSC) programs that were offered in some previous runs. DC&S proposals will be reviewed and prioritized independently from regular proposals to allow like-for-like comparison.

DC&S proposals have specific requirements and use a specific short proposal form (link to forms). Beamtime availability for this type of proposals is contingent on scheduling constraints and experiments are required to make use of one of the following frequently deployed configurations:

  • XCS: horizontal liquid jet for solution scattering and hard X-ray spectroscopy
  • MFX: horizontal liquid jet in helium/air for solution scattering or crystallography (may be combined with
  • X-ray emission spectroscopy and/or pump laser capabilities, dependent on availability)
  • MFX: droplet-on-tape sample delivery system for crystallography (may be combined with X-ray emission spectroscopy and/or pump laser capabilities, dependent on availability)
  • MFX: fixed targets in air
  • CXI: liquid jet in the microfocus chamber (no pump laser)
  • CXI: gas phase scattering in the microfocus chamber with 200 nm or 266 nm pump laser (only available for dataset collection experiments, not sample screening)
  • MEC: X-ray diffraction with uniaxial compression
  • MEC: X-ray imaging with long pulse laser side irradiation

Please contact Sandra Mous (smous@slac.stanford.edu) for additional information and guidance on DC&S proposals.

(3) Rapid Access proposals

Rapid Access proposals are welcome at any time during the Run cycle, although such access is constrained and dependent on the requested configuration's availability. Rapid Access proposals should typically target Standard Configurations and must articulate why urgent access is needed. Access has typically been aimed at structural biology studies (e.g. COVID research) but will be considered for any subject area with an appropriate case, subject to facility availability.

Modes of Beam Operation:

For up-to-date information on LCLS performance, please contact the respective instrument scientist listed above, and see the Machine FAQ and the Machine Parameters table, which includes a Multi-Color Pulse Mode Table.

***EDIT BELOW***

LCLS Scientific Department Head Contacts

For general inquiries when preparing proposals:

Submitting LCLS Proposals

LCLS encourages scientists from diverse fields and backgrounds to propose experiments utilizing the facility’s capabilities. New users are particularly welcome. Users are encouraged to review the LCLS instrument descriptions and contact LCLS staff to discuss technical capabilities and proposed experiments (see Scientific Department Head and Lead Instrument Scientist contacts above). These staff will provide advice on how to translate your scientific ideas into an LCLS experiment, and can help introduce new users to potential partner user groups if desired. Communication with the LCLS team is strongly encouraged to help maximize your chances of success.

Access to LCLS is open to the international community, with selection based on scientific merit. There is no charge to conduct experiments at LCLS, and the facility is able to help with the costs of performing experiments (e.g. consumables). However, users are responsible for their own travel expenses.

Register as a user and submit LCLS proposals through the Universal Proposal System (UPS)

Register here: https://ups.servicenowservices.com/ups

The Universal Proposal System (UPS) is a collaboration between the Advanced Photon Source (APS) at Argonne National Laboratory, the National Synchrotron Light Source II (NSLS-II) at Brookhaven National Laboratory, and the Linac Coherent Light Source (LCLS) at SLAC National Accelerator Laboratory. Registration in UPS is required for all members of the proposal team (Principal Investigator(s) and Co-Proposers).

Read the proposal preparation guidelines, along with information on new standard configurations, and the proposal review process prior to writing your proposal.

SSRL Beam Time tied to LCLS Experiments

For some LCLS proposals, the science case can be significantly enhanced by having access to SSRL beamtime in addition to proposed LCLS time. SLAC will consider a limited number of proposals that make a strong scientific case for beamtime access to SSRL. These proposals should indicate how much time is requested, when the time would be needed relative to the LCLS time, as well as which SSRL beamline would be needed. If users have questions about which SSRL beamlines would be appropriate for the proposed scientific goals, please contact Piero Pianetta (pianetta@slac.stanford.edu). Scheduling of time across facilities is complicated and availability depends strongly on which of the SSRL beamlines is requested.

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Timeline for Run 26

Run CycleProposal DeadlineCycle StartsCycle Ends
Run 26August 6, 2025 (4 pm Pacific)March 2026July 2026

A Virtual LCLS “Town Hall” User Meeting will be held at 9:00am Pacific Daylight Time on July 16, 2025.

This webcast meeting will be held to inform potential users about developments at LCLS before the upcoming LCLS proposal deadline. LCLS staff will inform the community about the latest capabilities and will be available for Q&A.