Run 21 Regular Proposals

Latest Proposal Schedule

Mode of Access Run Cycle Proposal Call Status Deadline Cycle Begins Cycle Ends
Regular User Proposal LCLS 22  Proposals under review. 28 Mar 2023 Jan 2024 Jun 2024
Data Set Collection (DSC) LCLS 22  Proposals under review. 28 Mar 2023 Jan 2024 Jun 2024
Protein Crystal Screening (PCS) LCLS 22  Proposals under review. 28 Apr 2023 Jan 2024 Jun 2024
MeV-UED Regular User Proposal UED 4 Experiments scheduled   Oct 2022 Jun 2023
Scientific Campaign Ongoing Experiments scheduled   Jan 2022 Jun 2022
Rapid Access LCLS 21   Contact for details

Proposals are submitted through the User Portal.

  Calls For Proposals are posted on the LCLS Annoucements, and e-mailed to the LCLS User Organization e-mail list (subscribe to lclsuo).

We are pleased to announce the call for LCLS Proposals for Run 21. It is anticipated that this will be the first time that beam from the new LCLS-II superconducting high repetition rate accelerator will be available.

For this Run, the superconducting accelerator is expected to be capable of up to 33 kHz. The existing copper accelerator will continue to be available, capable of up to 120 Hz.

The hard X-ray undulator will be served by the copper accelerator, providing vertical polarization and up to 25 keV X-rays in the fundamental, as well as rapid tuning / scanning capability using the variable gap system. This undulator will provide beam to the suite of hard X-ray instruments (XPP, XCS, MFX, CXI & MEC).

The soft X-ray undulator will primarily be served by the superconducting accelerator, providing beam to the soft X-ray instruments (TMO, ChemRIXS and qRIXS). The copper accelerator may still be used, if deemed necessary during commissioning.

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

For the soft X-ray instruments, an Early Science program is planned. User involvement should be initiated via a letter of interest, as described in the next section.

Early Science using LCLS-II with TMO, ChemRIXS, and qRIXS.

Following technical commissioning in Run 21, a period of ‘Early Science’ on each of these instruments will be organized and led by LCLS staff and will include interested members of the user community. These Early Science programs are intended to be pilot experiments that bridge between technical commissioning and regular user operations, and will replace the regular proposal submissions for Run 21.

  • TMO commissioning will focus on reestablishing operations with the high repetition rate LCLS-II X-ray beam at the existing TMO interaction point 1 (IP1) using the magnetic bottle spectrometer endstation. Toward the end of Run 21 we will begin the commissioning of TMO IP2 for the DREAM endstation. In between the two commissioning efforts we will have an Early Science period making use of LCLS-II capabilities in TMO IP1.
  • ChemRIXS commissioning will similarly focus on reestablishing operations with high repetition rate X-rays from LCLS-II, followed by an Early Science period.
  • qRIXS commissioning will seek to establish new capabilities in soft X-ray materials science for the first time. This is a complex process, such that the transition to Early Science may fall beyond the end of this Run.
  • A new OPCPA high repetition rate laser system will also be commissioned, with tailored capabilities for each instrument.

Regular ‘general user proposals’ are thus not sought for the soft X-ray instruments. If you are interested in participating in the Early Science programs in Run 21 (or for further information) please send a brief letter of interest by the Run 21 proposal deadline (March 30, 2022) to:

TMO:             James Cryan ( LCLS AMO Science Dept. Head, or Thomas Wolf ( LCLS Chemical Science Dept. Head
ChemRIXS:   Thomas Wolf ( LCLS Chemical Sci. Dept. Head
qRIXS:           Apurva Mehta ( LCLS Materials Science Dept. Head

Based on these letters of interest, an Early Science program will be announced to the user community no later than June 30, 2022. These experiments will be open to participation from the entire user community, with the objective of forming a broad, representative, expert team for each. Following this announcement in June, interested users should submit a description of their proposed contribution to specific experiments by September 1, 2022. Further detail will be supplied nearer the time.

Anticipating a successful Early Science period, TMO-IP1, ChemRIXS, and qRIXS will be made available for general user proposals using high repetition rate X-rays in the subsequent Run 22 period.

User proposals for the Hard X-ray Instruments

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 3rd March.

Standard Configurations: For Run 21, LCLS will continue to emphasize the use of Standard Configurations for the hard X-ray instruments, 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. 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.

Data Collection proposals are encouraged, where a single shift should be sufficient to produce a full data set suitable for publication using a suitable Standard Configuration. Those are submitted as regular proposals but should be marked as Data Collection in the title and can be shorter in length.

Rapid Access proposals are welcomed at any time during the Run cycle, although such access is highly constrained, dependent on the availability of the requested configuration. 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. Contact Mark Hunter ( for additional information and guidance about available setups.

Protein Crystal Screening (PCS) Proposals will be included in Run 21. A separate call for PCS proposals will be issued with a planned submission deadline in May 2022. For more information, please contact Mark Hunter (

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.

LCLS Instrument Contacts:

LCLS Scientific Department Head Contacts:

Submitting LCLS Proposals

The Linac Coherent Light Source (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 (see lists above) to discuss technical capabilities and proposed experiments. These staff will provide advice on how to translate your scientific ideas into an LCLS experiment. 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 User Portal

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

A Proposal Template has been created to provide guidance on the format and structure of proposal submissions. This template along with updated proposal preparation guidelines will also be discussed during the Virtual Town Hall.

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 ( Scheduling of time across facilities is complicated and availability depends strongly on which of the SSRL beamlines is requested.

Other Access Modes to LCLS

Science Campaigns. No new Science Campaigns are sought for Run 21.

Timeline for Run 21

Run Cycle Proposal Type Proposal Submission Deadline Run Cycle Begins Run Cycle Ends
LCLS 21 Regular User Proposal March 30, 2022 4 pm Pacific Oct 2022 May 2023
LCLS 21 Protein Crystal Screening (PCS) May 10, 2022 4 pm Pacific Oct 2022 May 2023

A Virtual LCLS “Town Hall” User Meeting will be held at 8:00am Pacific Daylight Time on March 3 2022.

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. Information on how to connect will be sent separately.