A New World Record: LCLS Approaches 100,000 Pulses Per Second On The Path To A Million

Experiments running at these higher pulse rates will allow scientists to capture ultrafast processes with greater precision, collect data more efficiently and explore phenomena that were previously out of reach.

Two years after teams at the Department of Energy’s SLAC National Accelerator Laboratory celebrated completion of the Linac Coherent Light Source (LCLS) upgrade project, LCLS-II, the X-ray laser has reached a major milestone: delivering 93 kHz – almost 100,000 pulses per second – a new world record for X-ray free-electron lasers. The achievement marks a critical step toward the machine’s goal of up to 1 million pulses per second, 8,000 times more than the original machine.

Experiments running at these higher pulse rates will allow scientists to capture ultrafast processes with greater precision, collect data more efficiently and explore phenomena that were previously out of reach. It transforms the ability of scientists to explore atomic-scale, ultrafast phenomena that are key to a broad range of applications, from quantum materials to energy technologies and medicine.

Every milestone brings us closer to delivering the science that LCLS-II was built to do. - John SchmergeDirector of SLAC’s Accelerator Directorate.

“For over a decade, we’ve planned a multi-year ramp to full power,” said John Schmerge, director of SLAC’s Accelerator Directorate. “It’s one thing to design the machine and build it, but ramping up the power is where you find out if everything really works the way it was designed to. Every milestone brings us closer to delivering the science that LCLS-II was built to do.”

Safely building up to 1 million pulses per second, or 1 MHz, requires a staged program of commissioning and power increases as the accelerator, undulators and experimental systems are qualified for higher duty cycles.

Accelerator teams are currently running LCLS at a rate of up to 33 kHz, or 33,000 pulses per second, for user experiments. Achieving this rate was already a major milestone, beating out the previous world record of 27,000 pulses per second held by the European XFEL.

“We ramp systematically because we don’t want to damage the machine,” Schmerge said. “The plan has always been to increase the beam power one safe step at a time. The approach is deliberate, methodical and essential for ensuring the reliability of the accelerator and the safety of the scientific instruments downstream.”

During the push to 93 kHz, teams from accelerator operations, radiation physics, machine protection, controls and beam diagnostics worked together in the accelerator control room. The result builds on a test earlier this year in which teams briefly reached 93 kHz at LCLS by lowering the beam charge to keep overall power constant. This new milestone achieves high pulse rate and high charge simultaneously, resulting in the most power the machine has produced to date.

“This is the first time the beam dump has ever absorbed this much power,” said SLAC Staff Scientist Yuantao Ding, who is overseeing the ramp-up. “We monitored everything live – beam loss, temperatures, cooling systems, cathode response. You make one change, you watch, you confirm. Then you take the next step.”

Beam power, a product of pulse charge and pulse rate, is a key limitation in safely operating superconducting accelerators. Increasing the power produced by LCLS allows accelerator physicists to make sure the machine performs the way it was designed to as it moves toward full-power operations.

“This is the first time we’ve reached such a high pulse rate and high charge,” Ding said. “We’ve done brief tests at even higher repetition rates before, but only at very low charge. Hitting 93 kilohertz this way is the meaningful benchmark. This is what will matter for user science.”

The milestone sets the stage for future experiments that depend on higher pulse rates. After teams increased the beam power, researchers at the Time-Resolved Atomic, Molecular and Optical Science (TMO) hutch at LCLS started an experiment to study how protons move inside molecules during light-driven reactions. Their technique involves exploding molecules and tracking the fragments to reconstruct how the atoms were arranged before the reaction.

“In order to ensure that we can understand the picture, we need to make sure there is a single molecule in the focus, so we do the experiments one molecule at a time,” said James Cryan, SLAC associate professor of photon science and TMO instrument lead. “This is quite time consuming to gather statistics, and thus the reliance on the high repetition rate.”

This is the last major pulse rate increase before teams begin preparing for the planned LCLS-II High-Energy (HE) upgrade, which will further boost electron beam energy and expand the accessible X-ray range. Everything the team learns now, Schmerge says, helps them hit the ground running when the high-energy upgrade starts.

“It’s exciting to finally see the machine deliver what it was built to do,” Schmerge added. “We’re not at a million pulses per second yet, but every step closer tells us we’re on the right path.”

LCLS is a DOE Office of Science user facility.

About SLAC
SLAC National Accelerator Laboratory explores how the universe works at the biggest, smallest and fastest scales and invents powerful tools used by researchers around the globe. As world leaders in ultrafast science and bold explorers of the physics of the universe, we forge new ground in understanding our origins and building a healthier and more sustainable future. Our discovery and innovation help develop new materials and chemical processes and open unprecedented views of the cosmos and life’s most delicate machinery. Building on more than 60 years of visionary research, we help shape the future by advancing areas such as quantum technology, scientific computing and the development of next-generation accelerators.

SLAC is operated by Stanford University for the U.S. Department of Energy’s Office of Science. The Office of Science is the single largest supporter of basic research in the physical sciences in the United States and is working to address some of the most pressing challenges of our time.