The Stanford Linear Accelerator Center (SLAC) has made groundbreaking discoveries over the years, but its recent development has made a one-mile stretch beneath Menlo Park colder than most of space.
A superconducting X-ray capable of taking videos of atoms could revolutionize science, not only in the large-scale analysis of molecules, but also in the improvement of everyday products such as telephone batteries and energy networks. , according to Mike Minitti, Senior Scientist. & Head of Soft X-Rays LCLS.
Such advances are possible now that SLAC has successfully brought the accelerator temperature down 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 in itself, but it is also a precursor for further development.
Dan Gonnella, head of the Superconducting Linac Physics Group, cites a shift in how scientists are able to analyze viruses and moving molecules in ways that could affect daily life. SLAC even participated in the imaging of the COVID-19 virus in the early stages of the pandemic.
“The users of this facility are very diverse. There’s a lot of biology work going on,” Gonella said. “There’s also a lot of materials science that would feed into new technologies, just in general, the technology of building this stuff is useful in other areas.”
So how does it work? The first step in this innovation is the cooling process. To keep the X-rays at such a low temperature, scientists lower the temperature of liquid helium from room temperature to just 2 degrees Kelvin, immobilizing the atoms.
This is done at the cryoplant. Two tonnes of helium gas are used for its operation and stored outside the plant. A liquid nitrogen truck is delivered daily to SLAC for this process.
The cooling process begins outside the cryogenic plant in what is called a “cold box”, where helium is mixed with oils for lubrication and compressed to begin lowering the temperature. Then the cold oil is removed because helium must be pure when it goes to the throttle.
The indoor cryogenic plant is driven by a control room on the machine floor in which 5,000 sensors and actuators send messages between the machines and the control room. It is inside that helium cools from 80 Kelvin to 4 Kelvin.
There are only six of these machines in the world, and two of them are on the SLAC campus.
SLAC has collaborated with several labs, including Jefferson Lab in Virginia and Fermi Lab in Illinois.
One of SLAC’s two helium cooling systems is currently operating, and the second is expected to be commissioned this summer.
The LCLS-II is found underground right next to the cryoplant. Above the conductor, a metal building called the gallery houses the machinery necessary to keep everything running smoothly, stretching for 3 kilometers, so long that no end can be seen.
SLAC scientists ripped out 1 kilometer of the old copper accelerator and installed the superconducting accelerator in its place.
Liquid helium from the cryogenic plant enters the distribution box in the gallery before passing through a network of valves and circuits inside the distribution box. From there, helium is pushed into the underground tunnel housing LCLS-II, according to Gonnella.
In the tunnel there are 37 orange tubes called cryomodules which are responsible for accelerating electrons. Inside each cryomodule is a gray structure made of niobium, a superconductor. The niobium is responsible for the acceleration while the cryomodules keep the helium at -456 F, nearly 100 degrees cooler than Pluto.
“It’s much more efficient from an energy perspective,” 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 activated, it is able to stay on, unlike the old accelerator which was only able to run for a few milliseconds. If the old equipment, of which 1 kilometer is still in use, is left on longer, it will overheat and melt quickly, while the new one is able to operate for longer periods of time and can not only take images of atoms but also take videos. .
LCLS-II operates at 4 billion electron-volts per second, and the plan is to increase this 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 the gigavolts of LCLS-II.
“The way I like to think about it is that in the doctor’s office the x-ray machine is (smaller) and it can look at your teeth, but here it’s a mile long so it can look at the atoms,” Gonnella said. “It sort of evolves that way, the bigger you get, the more you can look at smaller things.”
SLAC plans to reach 8 billion electron volts over the next six years, and its staff is already working on adding cryomodules.
Five kilometers from the cryousine is one of SLAC’s seven experimental stations. Here, superconducting science is able to impact everyday life.
“It’s huge because it’s important for (different) kinds of energy, like advanced materials that make better memories for your camera, better optics, just better, faster computers,” he said. said Minitti. “It revolutionized the way we look at viruses… when COVID hit, we got emergency use from the (US) Department of Energy to study the structure of COVID-19 and that helped shed light on some of the these RNA studies.”
“The technology that superconducting technology will enable is our ability to track electronic or molecular dynamics in new materials,” Minitti said. “These materials will go to your computer, will go to your battery, so if we can think of ways to optimize this material…it makes your power grid more efficient, extends the life of your battery.”
However, the experimental benefits of superconducting technology go beyond the images that X-rays analyze. SLAC scientists have been researching ways to use superconducting technologies at higher temperatures to improve energy networks. If it were possible to run this same technology at higher temperatures, it could be used to reduce or eliminate the energy lost during transmission, Minitti said. As it stands, this can only be achieved in cold conditions.
For the moment, superconductivity consumes too much energy to feed itself.
One of the advantages 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 old linear accelerator, there was always a long wait for X-rays to perform experiments. With recent developments, more researchers should be able to use the LCLS-II at a time, and the experimental laboratory may expand for additional research in the future.
Experimental stations allow scientists to analyze molecules in ways that can impact our understanding of their structure, by observing 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 influence each other. The experiment should be operational soon, according to Minitti.
SLAC continues to use the LCLS-II for experiments that monitor how atoms and molecules move and interact with each other, giving researchers a better understanding of the nature of subatomic particles.
“It’s re-revolutionized the landscape of free-electron and X-ray science, so it’s good to have it here in our backyard,” Minitti said.