Fermi Lab completes the phased work of SLAC X-ray laser upgrade project

The US Department of Energy's Fermi National Accelerator Laboratory (Fermilab) has successfully completed the construction and delivery of the final key component provided for the SLAC National Accelerator Laboratory's Coherent Light Source (LCLS) high-energy upgrade project. As the world's most powerful X-ray free electron laser (XFEL), the upgrade of LCLS will further enhance its research capabilities and help cutting-edge scientific research reach a new level.

Fermilab’s contributions have been crucial for the superconducting accelerator for LCLS, which enables x-ray laser beams that are 10,000× brighter with pulses that arrive up to a million times per second. The high-energy upgrade will add 23 cryomodules to the superconducting accelerator, doubling the energy of the beam and more than doubling the maximum x-ray energy.

The upgraded LCLS linac uses superconducting radio-frequency technology to power an electron beam to high energies. The beam is sent through special magnets called undulators to make it jiggle, creating x-rays. As the x-rays and electron beam move together and interact, they produce coherent radiation.

SLAC Director John Sarrao (left) and Fermilab Director Norbert Holtkamp sign their names on the final Fermilab cryomodule. Its completion marks a milestone for the high-energy LCLS upgrade. 

“It’s sort of the same process that you have in a laser pointer, but now it’s in an accelerator,” said Genfa Wu, who has led the Fermilab scope of LCLS upgrades since 2024. “And instead of producing visible light, it produces coherent photons in the x-ray spectrum.”

Those X-rays are routed to scientific end-stations along the linac. LCLS-enabled experiments address fundamental questions in energy storage, catalysis, biology, materials science and quantum physics.

The current upgrade, called LCLS-II High Energy, will double the energy of the x-ray laser. But when it was first being planned, teams realized it wouldn’t be possible to reach those higher energies in the limited space left in the linac tunnel with the current technology. So, they had to innovate.

Accelerator experts at SLAC, Jefferson Lab, Cornell University, and Fermilab combined forces to figure out how to improve the cryomodules. They targeted the superconducting accelerator cavities, the components inside the cryomodules that accelerate the particle beam. Through a process called “nitrogen doping,” they optimized the molecular makeup of the walls of the cavities, and they developed new procedures to assemble and finish the components. They also improved the cleanliness to reduce unwanted effects from any contamination on the surface, including errant dust particles.

“Fermilab didn’t just build the cryomodules — we developed the enabling technologies at the heart of these components, and we were the Designer of Record for the cryomodules,” said Sam Posen, associate lab director for the Applied Physics and Superconducting Technology division at Fermilab.

Source: photonics