The new LCLS-II facility will refine our understanding of how nature operates on ultra-small, ultrafast scales, with implications ranging from quantum gadgets to clean energy.
An 800-meter long tunnel, 9 Meters underground in Menlo Park, California, is now colder than the rest of the cosmos. It houses a new superconducting particle accelerator as part of a project to enhance the Department of Energy’s SLAC National Accelerator Laboratory’s Linac Coherent Light Source (LCLS) X-ray free-electron laser.
Crews successfully cooled the accelerator to minus 235 degrees– or 2 kelvins – a temperature at which it becomes superconducting and can boost electrons to high energies with nearly zero energy lost in the process. It is one of the last milestones before LCLS-II will produce X-ray pulses that are 10,000 times brighter, on average, than those of LCLS and that arrive up to a million times per second – a world record for today’s most powerful X-ray light sources.
“In just a few hours, LCLS-II will produce more X-ray pulses than the current laser has generated in its entire lifetime,” says Mike Dunne, director of LCLS. “Data that once might have taken months to collect could be produced in minutes. It will take X-ray science to the next level, paving the way for a whole new range of studies and advancing our ability to develop revolutionary technologies to address some of the most profound challenges facing our society.”
Scientists can examine the details of complex materials with unprecedented resolution to drive new forms of computing and communications; reveal rare and fleeting chemical events to teach us how to create more sustainable industries and clean energy technologies; investigate how biological molecules carry out life’s functions to develop new types of pharmaceuticals; and peer into the bizarre world of quantum mechanics by directly measuring them.
A chilling feat
LCLS, the world’s first hard X-ray free-electron laser (XFEL), produced its first light in April 2009, generating X-ray pulses a billion times brighter than anything that had come before. It accelerates electrons through a copper pipe at room temperature, which limits its rate to 120 X-ray pulses per second.
The LCLS-II improvement project began in 2013, with the goal of increasing the rate to a million pulses per second and making the X-ray laser thousands of times more intense. Crews removed a section of the old copper accelerator and replaced it with a set of 37 cryogenic accelerator modules that house pearl-like strings of niobium metal cavities. The niobium cavities are surrounded by three nested levels of cooling equipment, each one lowering the temperature until it approaches near absolute zero, at which point the niobium cavities become superconducting.
“Unlike the copper accelerator powering LCLS, which operates at ambient temperature, the LCLS-II superconducting accelerator operates at 2 kelvins, only about 4 degrees Fahrenheit above absolute zero, the lowest possible temperature,” said Eric Fauve, director of the Cryogenic Division at SLAC. “To reach this temperature, the linac is equipped with two world-class helium cryoplants, making SLAC one of the significant cryogenic landmarks in the U.S. and on the globe. The SLAC Cryogenics team has worked on site throughout the pandemic to install and commission the cryogenic system and cool down the accelerator in record time.”
Bringing it to life
In addition to a new accelerator and a cryoplant, the project required other cutting-edge components, including a new electron source and two new strings of undulator magnets that can generate both “hard” and “soft” X-rays. Hard X-rays, which are more energetic, allow researchers to image materials and biological systems at the atomic level. Soft X-rays can capture how energy flows between atoms and molecules, tracking chemistry in action and offering insights into new energy technologies. To bring this project to life, SLAC teamed up with four other national labs – Argonne, Berkeley Lab, Fermilab and Jefferson Lab – and Cornell University.
Jefferson Lab, Fermilab and SLAC pooled their expertise for research and development on cryomodules. After constructing the cryomodules, Fermilab and Jefferson Lab tested each one extensively before the vessels were packed and shipped to SLAC by truck. The Jefferson Lab team also designed and helped procure the elements of the cryoplants.
Photo Credit: SLAC National Accelerator Laboratory