LCLS Call for Proposals for Run 21

By pjones
January 31, 2022

Call for Proposals - Run 21
Linac Coherent Light Source - SLAC National Accelerator Laboratory

Deadline: 4:00 p.m. Pacific Daylight Time (PDT) 30 March 2022
This call is for experiments to run from October 2022 through May 2023

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.

LCLS encourages scientists from diverse fields and backgrounds to propose experiments utilizing the facility’s capabilities. New users are particularly welcome.

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.

For full details of the call, please visit:



Soft X-ray Instruments

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

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

Following technical commissioning in Run 21, a period of ‘Early Science’ on the TMO, ChemRIXS, and qRIXS 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.

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:

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.

Hard X-ray Instruments

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

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.

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.

Other Access Modes to LCLS

Data Collection

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

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

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 (

Science Campaigns

No new Science Campaigns are sought for Run 21.

Modes of Beam Operation

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

LCLS Instrument Contacts:

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.

LCLS Virtual Town Hall on Run 21 Regular Proposals

On Thursday, 03 March 2021, LCLS will host a virtual “Town Hall” meeting to inform the user community about the latest technical developments at LCLS. This interactive webinar includes a series of short talks by LCLS staff, with interactive Q&A throughout and open questions at the end of the session. The whole community is invited to participate.

For more general information about LCLS, please visit:

I look forward to seeing your proposals!
Many thanks,

Mike Dunne
Director, LCLS