New upgrade will supercharge atomic vision of the world’s most powerful X-ray laser

The Department of Energy (DOE) has given the green light for construction to begin on a high-energy upgrade that will further boost the performance of the Linac Coherent Light Source (LCLS), the world’s most powerful X-ray free-electron laser (XFEL) at the DOE’s SLAC National Accelerator Laboratory.

When complete, the upgrade will allow scientists to explore atomic-scale processes with unprecedented precision and address fundamental questions in energy storage, catalysis, biology, materials science and quantum physics like never before.

“This high-energy upgrade to LCLS strengthens the lab’s position as a world leader in X-ray and ultrafast science,” said SLAC Lab Director John Sarrao. “With the critical support of the Department of Energy’s Office of Science and our partner labs, the upgrade, when complete, will open new avenues for scientific discovery and innovation. This will continue to attract top talent and foster groundbreaking research across multiple disciplines.”

In 2023, SLAC celebrated completion of the LCLS-II project, taking X-ray science to a whole new level with the addition of a superconducting accelerator, two new magnetic structures, called undulators, to generate soft and hard X-rays from the electron beam, and other major leaps in technology that allow the facility to produce up to a million X-ray pulses per second—8,000 times more than its predecessor.

The new upgrade project, called LCLS-II-HE, will double the energy of the electron beam coming out of the superconducting electron accelerator, which will more than double the maximum X-ray energy and deliver a 3,000-fold performance increase in average X-ray brightness for “hard,” or high-energy, X-rays.

“The LCLS-II-HE upgrade will be a transformative advance for the scientific mission of DOE Basic Energy Sciences and the broader scientific community,” said LCLS Director Mike Dunne. “If the LCLS-II upgrade enabled a high-quality movie camera capable of capturing clear and detailed images, the LCLS-II-HE upgrade greatly boosts that camera’s resolution and sensitivity.

“Scientists will be able to image the atomic-scale motion of materials, chemical systems and biological complexes to address some of the most critical challenges facing our society.”

With favorable Critical Decisions 2 and 3 (CD-2/3) in September 2024, DOE has formally approved construction of the $716M project, representing a significant advancement in X-ray laser technology.

Teaming up with partner labs for higher power

When LCLS turned on in 2009, it was the world’s first free-electron laser producing hard X-rays. Since then, similar light sources have sprung up around the world. The LCLS-II upgrade significantly boosted the facility’s power beyond anything else in the world.

The new superconducting accelerator built as part of the LCLS-II upgrade comprises 37 cryogenic modules that are cooled to -456°F—colder than outer space—a temperature at which it can boost electrons to high energies with nearly zero energy loss.

The cryomodules were designed by DOE’s Fermi National Accelerator Laboratory (Fermilab), who partnered with Thomas Jefferson National Accelerator Facility (Jefferson Lab) to share their construction and testing. Lawrence Berkeley National Laboratory (Berkeley Lab) and Argonne National Laboratory designed the undulators which are used to produce the X-rays.

SLAC has teamed up with these national labs, along with the Facility for Rare Isotope Beams (FRIB) at Michigan State University, once again for the LCLS-II-HE upgrade project. A set of 23 new cryomodules are being built and tested by Fermilab and Jefferson Lab, each containing eight superconducting radiofrequency cavities that implement the latest technology for enhanced performance.

The high-energy upgrade will use the existing hard X-ray undulator and SLAC will partner with Berkeley Lab again to modify the soft X-ray undulator so that both can be used simultaneously with the new beam.

Fabrication and delivery of the cryomodules are already well underway, thanks to prior approval by the DOE to procure these long-lead-time components to be ready to start installation in the SLAC accelerator tunnel by the end of 2025. To date, about 95% of the cavities have been produced and 10 cryomodules delivered to SLAC.

Tests indicate that these should achieve a performance level at least one and a half times higher than the cryomodules produced for the LCLS-II upgrade, showing the rapid pace of change in this field.

“Teamwork and collaboration drive the groundbreaking advancements in XFEL technology, enabling unprecedented exploration of atomic and molecular structures at ultrafast timescales,” said LCLS-II-HE Project Director Greg Hays.

“This collective effort harnesses the expertise of hundreds of scientists, engineers, and technicians across the nation, building on long-standing partnerships with experts from around the world. The DOE Office of Science has a proud history of successful completion of complex, large-scale projects. The LCLS-II-HE upgrade is the latest in this line, and we’re excited to move into this final phase of delivery.”

High energy opens new doors for science

The LCLS-II-HE upgrade will enable deep insights into the atomic level dynamics that underpin the function of much of the complex world around us—from clean energy, to sustainability, to advanced manufacturing and human health. Solutions in these areas depend on a transformation in our predictive understanding and ability to control complex matter, materials and devices at the fundamental time and length scales that determine how they function.

For example, with hard X-rays and the higher sensitivity made possible by the upgrade, scientists will be able to look deep into solid and liquid systems to study hidden surfaces, dissolved molecules, and nanomaterials. This ability is crucial for developing new ideas for renewable energy and catalysts to help design efficient systems for sustainable manufacturing, energy storage, and solar energy conversion into carbon-free fuels and electricity.

In the field of biomedical science, a much deeper understanding is needed that links the structural evolution of a biomolecular system to its function. This is crucial for human health and biosecurity, and to inform synthetic approaches for harnessing biochemical approaches for green industrial, agricultural and energy solutions.

With the high-energy upgrade, LCLS will be able to map the full range of motions of biological samples as they function—and do so in physiologically relevant environments for the first time, driving the design of new targeted pharmaceuticals that can more effectively treat diseases.

The upgrade will provide high-resolution tools to capture the behavior of new types of materials and quantum systems, driving the design of a new generation of ultrafast computers and communications systems, and aiming to significantly reduce energy consumption in data centers and improve the energy efficiency of electronic devices.

An enhanced LCLS will also advance machine learning and AI by generating unprecedented amounts of high-quality data that can be used to train more accurate models and accelerate scientific discoveries—over a petabyte of data per day, equivalent to a million movie downloads. It will enable predictive modeling, autonomous experimentation, and the development of new algorithms, enhancing data analysis across each of these scientific fields.