Stanford Linear Accelerator Center (SLAC) has made revolutionary discoveries over the years, but its recent development has made a 1-kilometer stretch under Menlo Park colder than most of space.

A superconducting X-ray able to take videos of atoms can revolutionize science, not just at the grand scale of analyzing molecules, but in improving everyday products such as phone batteries and energy grids, according to Mike Minitti, senior staff scientist & LCLS Soft X-ray department head.

Such advances are possible now that SLAC has successfully lowered the temperature of the accelerator to 2 Kelvin, or -456 F, which is lower than the coldest point in our solar system, Uranus at -371 F.

The superconducting accelerator, known as the Linac Coherent Light Source (LCLS-II) is an innovation itself, but it's also a precursor for further development.

Dan Gonnella, leader of the Superconducting Linac Physics Group, cites a change in the way that scientists are able to analyze viruses and molecules in motion in ways that could affect daily life. SLAC even had a hand in imaging the COVID-19 virus in the early stages of the pandemic.

"The users of this facility are a wide spectrum. There's a lot of biology work that goes on," Gonella said. "There's also a lot of material science that would feed into new technology, just in general, the technology from building these kinds of things is useful in other fields."

So how does it work? The first step in this innovation is the cooling process. To keep the X-ray at such a drastically low temperature, scientists lower the temperature of liquid helium from room temperature to only 2 degrees Kelvin, putting the atoms at a near standstill.

This is done at the cryoplant. Two tons of gaseous helium are used in its operation and stored outside the plant. One truck of liquid nitrogen is delivered to SLAC every day for this process.

The cooling process begins outside the cryoplant in what is called a "cold box," where the helium is mixed with oils for lubrication and compressed to begin lowering the temperature. Then the cold oil is removed since the helium has to be pure when it goes to the accelerator.

The interior cryoplant is run by a control room upstairs from the machinery in which 5,000 sensors and actuators send messages between the machines and the control room. Inside is where the helium cools from 80 Kelvin to 4 Kelvin.

There are only six of these machines in the world, and two of them are at SLAC's campus.

SLAC collaborated with several labs including Jefferson Lab in Virginia and Fermi Lab in Illinois.

One of SLAC's two systems to chill helium is currently running and the second should be turned on this summer.

The accelerator

The LCLS-II sits below ground right beside the cryoplant. Above the conductor, a metal building called the gallery holds the machinery required to make everything run smoothly, stretching 3 kilometers, so long that you're not able to see either end.

Scientists at SLAC have torn out 1 kilometer of the old copper accelerator and installed the superconducting accelerator in its place.

The liquid helium from the cryoplant comes to the distribution box in the gallery before flowing through an array of valves and circuits within the distribution box. From there, the helium is pushed down into the underground tunnel housing LCLS-II, according to Gonnella.

In the tunnel, there are 37 orange tubes called cryomodules that are responsible for the acceleration of the electrons. Inside each cryomodule is a gray structure made of niobium, a superconductor. The niobium is responsible for the acceleration while the cryomodules hold helium at -456 F, nearly 100 degrees colder than Pluto.

"It's much more efficient from an energy standpoint," Gonnella said. "So one of the benefits of building this accelerator is what we can get out of it compared to if you had the old one."

When LCLS-II is turned on, it's able to stay on, as opposed to the old accelerator which was only capable of running for milliseconds. If the older equipment, 1 kilometer of which is still in use, is left on for longer, it would quickly overheat and melt, whereas the new one is capable of running for longer periods and can not only snap images of atoms but also take videos.

LCLS-II operates at 4 billion electron volts a second, and the plan is to increase that in the future. Higher levels of electron volts correspond to stronger X-rays. For context, an X-ray in the doctor's office runs on kilovolts, a million times less powerful than LCLS-II's gigavolts.

"The way I like to think about it is in the doctor's office the X-ray machine is (smaller) and it can look at your teeth, but here, it's a kilometer long so it can look at atoms," Gonnella said. "It kind of scales that way, the bigger you get, you can look at smaller things."

SLAC plans to reach 8 billion electron volts in the next six years, and its staff is already working on adding cryomodules.

The experiments

Three miles away from the cryoplant is one of SLAC's seven experimental stations. Here, the superconducting science is able to have impacts on daily life.

"This is huge because it's big for the (different) types of energy, like frontier materials that make better memories for your camera, better optics, just better, faster computers," Minitti said. "It revolutionized the way we look at viruses ... when COVID hit we got emergency use from the (U.S.) Department of Energy to study the structure of COVID-19 and that helped inform some of these RNA studies."

"The technology that superconducting technology will enable is our ability to track electron or molecular dynamics in new, novel materials," Minitti said. "Those materials will go to your computer, go to your battery, so if we can think of ways of optimizing that material ... that makes your power grid more efficient, makes your battery last longer."

However, the experimental benefits of superconducting technology go beyond the images that the X-ray analyzes. Scientists at SLAC have been researching ways of using superconducting technologies at higher temperatures to improve energy grids. If it was possible to run this same technology at higher temperatures, it could be used to reduce or eliminate energy lost during transmission, Minitti said. As it stands, this can only be achieved in cold conditions.

For now, superconductivity takes too much energy to power itself.

One benefit of the superconducting accelerator is that it is able to send data to more than one experiment at a time, according to Gonnella. At the previous linear accelerator, there was always a long wait for time for the X-ray to run experiments. With recent developments, more researchers should be able to use the LCLS-II at once, and the experimental lab can expand for additional research in the future.

The experimental stations allow scientists to analyze the molecules in ways that can impact our understanding of their structure, watching electrons and nuclei respond to energy. SLAC even has the first experimental station that can combine two free-electron lasers at once, seeing how they interact and affect each other. The experiment should be up and running soon, according to Minitti.

SLAC continues to use the LCLS-II for experiments that monitor the way that atoms and molecules move and interact with each other, giving researchers a better understanding of the nature of subatomic particles.

"This has re-revolutionized the landscape of free electron and X-ray science, so it's nice to have it here in our backyard," Minitti said.