Building the world's brightest X-ray laser

The LCLS-II laser will be 10,000 times brighter than its predecessor.

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Andy Altman
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Thirty feet underground and a stone's throw from Stanford University, scientists are putting the finishing touches on a laser that could fundamentally change the way they study the building blocks of the universe.

When completed next year, the Linac Coherent Light Source II, or the LCLS-II , will be the second world-class X-ray laser at the Department of Energy's SLAC National Accelerator Laboratory. CNET was given the rare opportunity to film inside the more than 2-mile long tunnel ahead of the new laser's launch. Click the video above to learn more.

The first LCLS, in operation since 2009, creates a beam capable of 120 light pulses per second. The LCLS-II will be capable of up to 1 million pulses per second, and a beam 10,000 times brighter than its predecessor. 


In the underground tunnel at the LCLS.

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"I think it's absolutely fair to say that the LCLS-II will usher in a new era of science," says Dr. James Cryan, a staff scientist at SLAC.  He says the laser will make previously impossible experiments possible. 

You can think of the LCLS as being like a microscope with atomic resolution. At its core it is a particle accelerator, a device that speeds up charged particles and channels them into a beam. That beam is then run through a series of alternating magnets (a device called an undulator) to produce X-rays. Scientists can use those X-rays to create what they call molecular movies. These are snapshots of atoms and molecules in motion, captured within a few quadrillionths of a second, and strung together like a film. 


Looking down Undulator Hall, a 100-meter stretch of alternating magnets that convert electron beams into X-rays.

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Scientists across nearly every scientific field have come from all over the world to run their experiments with the LCLS. Among other things, their molecular movies have shown chemical reactions as they happened, demonstrated the behavior of atoms inside stars, and produced live snapshots detailing the process of photosynthesis.

The LCLS-II and its higher pulse rate become a game changer for these molecular movies, according to Andrew Burrill, SLAC associate lab director. 

"If you think about a strobe light that goes off 120 times, you see one image. If it goes off a million times in a second, you get a much different image. So you can create a much better movie," he says.

Though both lasers accelerate electrons to nearly the speed of light, they'll each do it differently. The LCLS's accelerator pushes the electrons down a copper pipe that operates at room temperature, designed to be activated only in short bursts. But the LCLS-II is designed to run continuously, which means it generates massive amounts of heat. A copper cavity would absorb too much of that heat. That's why engineers turned to a new superconducting accelerator, composed of dozens of 40-foot-long devices called cryomodules designed to run at two degrees above absolute zero (-456 degrees Fahrenheit). They're kept at operating temperature by a massive cryogenics plant above ground.


A series of superconducting cryomodules that operate at -456 Fahrenheit accelerate electrons to nearly the speed of light.

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Cryan says the LCLS-II will allow SLAC scientists answer questions they've been trying to solve for years. "How does energy transfer happen inside molecular systems? How does charge transfer happen? Once we understand some of these principles, we can start to apply them to understand how we can do artificial photosynthesis, how can we build better solar cells."

Scientists at SLAC hope to produce their first electron beam with the LCLS-II in January, followed by their first X-ray in the summer, which they'll refer to as their first "big light" event.