X-Ray Laser Achieves Its Final, Colder-Than-Space Temperature

The superconducting particle accelerator, an upgrade to the Linac Coherent Light Source (LCLS) x-ray free-electron laser at the U.S. Department of Energy’s SLAC National Accelerator Laboratory, has been cooled to a temperature of −456 °F, or 2 K. At this temperature, the particle accelerator becomes superconducting and can boost electrons to high energies with nearly zero energy lost in the process.

Though the accelerator reached its final temperature of 2 K in April, SLAC reported May 10 that the accelerator was ready for initial operations.

The achievement marks one of the last milestones before LCLS-II will produce x-ray pulses that are 10,000× brighter, on average, than those of LCLS. The pulses are also poised to arrive up to 1 million times per second. From these capabilities, 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 help create more sustainable industries and clean energy technologies, study how biological molecules carry out life’s functions to develop new types of pharmaceuticals, and study quantum mechanics by directly measuring the motions of individual atoms.

“In just a few hours, LCLS-II will produce more x-ray pulses than the current laser has generated in its entire lifetime,” said Mike Dunne, director of LCLS. “Data that once might have taken months to collect could be produced in minutes.”

The LCLS-II facility will soon be ready to emit the world’s most powerful bursts of x-rays, which will help scientists study how nature works on ultrasmall, ultrafast scales, affecting everything from quantum devices to clean energy. Courtesy of SLAC National Accelerator Laboratory.

Once the system is operational, which is planned to happen this year, it will emit the world’s most powerful bursts of x-rays. Scientists will be able to use the two x-ray lasers in parallel to conduct experiments over a wider energy range, capture detailed snapshots of ultrafast processes, probe delicate samples, and gather more data in less time, which will increase the number of experiments that can be performed.

LCLS produced its first light in 2009, generating x-ray pulses 1 billion times brighter than anything that had come before. LCLS accelerates electrons through a copper pipe at room temperature, which limits its rate to 120 x-ray pulses per second.

In 2013, SLAC launched the LCLS-II upgrade project to boost that rate to 1 million pulses and make the x-ray laser thousands of times more powerful. Crews installed a series of 37 cryogenic accelerator modules, which house pearl-like strings of niobium metal cavities. These are surrounded by three nested layers of cooling equipment, and each successive layer lowers the temperature until it reaches nearly absolute zero — a condition at which the niobium cavities become superconducting.

The linac is equipped with two helium cryoplants, one of which cools helium gas from room temperature to its liquid phase at just a few degrees above absolute zero, providing the coolant for the accelerator. In addition to a new accelerator and a cryoplant, teams also added a new electron source and two new strings of undulator magnets that can generate both hard and soft x-rays.

Hard x-rays 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 energy technologies.

The linac is equipped with two helium cryoplants. One of these cryoplants cools helium gas from room temperature to its liquid phase at just a few degrees above absolute zero, providing the coolant for the accelerator. Courtesy of Greg Stewart/SLAC National Accelerator Laboratory.

With the cavities cooled, researchers will pump them with more than 1 MW of microwave power to accelerate the electron beam from the new source. Electrons passing through the cavities will draw energy from the microwaves so that by the time the electrons have passed through all 37 cryomodules, they will be moving close to the speed of light. The electrons will then be directed through the undulators, forcing the electron beam on a zigzag path.

The project is supported by Department of Energy’s Office of Science.