World's most powerful free-electron laser upgraded to fire a million X-rays per second

US DoE particle will be a 'strobe light' in atomic disco

The world's most powerful publicly known X-ray laser at the US Department of Energy's SLAC National Accelerator Laboratory has fired its first pulses with an upgrade that could see it scan our world in strange new ways.

After a decade of effort, the lab's Linac Coherent Light Source (LCLS) atomic X-ray free-electron laser has been upgraded and can deliver up to a million pulses per second, each up to 10,000 times brighter than those emitted by previous instruments - making it 8,000 times more powerful than its predecessor. Or so Uncle Sam says.

"The wavelength of these X-rays is about the size of an atom, so the X-ray laser can track the internal structure of a molecule. And because the X-rays arrive in an ultrafast burst - femtosecond, a millionth of a billionth of a second - then we can 'freeze frame' the motion – similar to a strobe light in a disco," Mike Dunne and Greg Hays, the LCLS director and LCLS-II project director, explained to The Register.

"So we build up a stop-motion movie of how the world around us works at this atomic molecular scale – following a chemical reaction in real time, or watching the emergence of a quantum phenomenon like superconductivity."

The new LCLS-II generates a pulse of ultraviolet light that collides with a photocathode to release a cascade of electrons. These electrons are accelerated close to the speed of light by traveling through a series of 37 cryogenic modules containing superconducting magnets cooled down to minus 456 degrees Fahrenheit (minus 271 degrees Celsius). 

The beam is directed onto whatever sample scientists want wish to probe. The X-rays penetrate the molecule and are diffracted to create a pattern that reveals details of their structure. Having a more powerful X-ray laser allows scientists to capture detailed snapshots more quickly, giving them the ability to see how materials or chemical processes unfold in real time.

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"The light from SLAC's LCLS-II will illuminate the smallest and fastest phenomena in the universe and lead to big discoveries in disciplines ranging from human health to quantum materials science," US Secretary of Energy Jennifer Granholm said in a statement.

The improved X-ray laser has been fitted with two cryoplants - kit that produces liquified helium gas and pumps it around the particle accelerator. It also boasts a pair of undulators to produce X-rays from the electrons, plus more sensitive detectors and sensors with the processing power to handle the instrument, and the data it generates, swiftly. 

LCLS-II produces X-rays at "hard" and "soft" wavelengths (high or low-energy respectively) that can probe objects at different levels, ranging from pharmaceutical molecules to quantum materials. Scientists will employ the laser to examine processes like photosynthesis or interactions between atoms in condensed matter.

"Soft-X-rays are useful for looking at where the electrons are in a molecule (and so tell us about how energy and charge are moving about - for example if we want to optimize how to harness energy from the sun. Hard X-rays tell you about where the atoms are – the structure of the material – and so are useful for looking at how the world around us is constructed. A good example is the structure of a protein and the pharmaceuticals used to treat disease," Dunne and Hays said.

Scientists will begin conducting experiments using the instrument in the next few weeks, and others can submit proposals for time using the laser. There are only a handful of free-electron X-ray laser facilities around the world in the US, Europe, and Asia, so get a proposal in fast.

"I really look forward to the impact of LCLS-II and the user community on national science priorities, ranging from fundamental science research in chemistry, materials, biology, and more; application of the science advances for clean energy; and ensuring national security through initiatives like quantum information science," DOE Office of Science Director Asmeret Asefaw Berhe added. ®

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