by A particle accelerator that binds electrons here on Earth has reached temperatures colder than those in outer space.
Using the bone scan free-electron laser at the Department of Energy’s SLAC National Accelerator Laboratory, part of a Linac Coherent Light Source (LCLS) upgrade project, called LCLS II, scientists cooled liquid helium to minus 456 degrees Fahrenheit (minus 271 degrees Celsius), or 2 Kelvin. That’s just 2 kelvins above absolute zero, the coldest possible temperature at which all particle motion ceases. That icy environment is crucial for the accelerator, because at such low temperatures the machine becomes superconducting, meaning it can push electrons through it with almost zero energy loss.
Even the empty regions of space are not so cold, as they are still filled with the cosmic microwave background radiation, a remnant from shortly after the big Bang having a uniform temperature of minus 454 F (minus 271 C), or 3 K.
“The LCLS-II X-ray free electron laser next-generation superconducting accelerator has reached its operating temperature of 2 degrees above absolute zero,” Andrew Burrill, director of SLAC’s Directorate of Accelerators, told WordsSideKick.com. .
LCLS-II is now ready to start accelerating electrons to 1 million pulses per second, which is a world record, he added.
“This is four orders of magnitude more pulses per second than its predecessor, LCLS, which means that, in just a few hours, we will have delivered more X-rays to users. [who aim to utilize them in experiments] what LCLS has done in the last 10 years,” Burrill said.
This is one of the last milestones LCLS-II must reach before it can produce X-ray pulses that are, on average, 10,000 times brighter than those created by its predecessor. This should help researchers probe complex materials in unprecedented detail. High-intensity, high-frequency laser pulses allow researchers to see how electrons and atoms in materials interact with unprecedented clarity. This will have a number of applications, from helping to reveal “how natural and artificial molecular systems convert sunlight into fuels, and thus how to control these processes, to understanding the fundamental properties of materials that will enable quantum computing.” Burill said. .
Related: 10 cosmic mysteries the Large Hadron Collider could unravel
Creating the icy climates inside the accelerator required some work. To prevent helium from evaporating, for example, the team needed very low pressures.
Eric Fauve, director of SLAC’s Cryogenics Division, told Live Science that at sea level, pure water boils at 212 F (100 C), but this boiling temperature varies with pressure. For example, in a pressure cooker, the pressure is higher and the water boils at 250°F (121°C), while the opposite occurs at altitude, where the pressure is lower and the water boils at a temperature more low.
“For helium, it’s very much the same. However, at atmospheric pressure, helium boils at 4.2 kelvins; this temperature will drop if the pressure drops,” Fauve said. “To get the temperature down to 2.0 Kelvin, we need to have a pressure of only 1/30 of atmospheric pressure.”
To achieve these low pressures, the team uses five cryogenic centrifugal compressors, which compress helium to cool it and then let it expand in a chamber to reduce pressure, making it one of the few places where land where 2.0 K helium can be produced on a large scale.
Fauve explained that each cold compressor is a centrifugal machine equipped with a rotor/impeller similar to that of an engine turbocharger.
“As it spins, the impeller accelerates the helium molecules creating a vacuum in the center of the wheel where the molecules are sucked in, creating pressure on the periphery of the wheel where the molecules are ejected,” he said.
The compression forces the helium into its liquid state, but the helium escapes into this vacuum, where it expands rapidly, cooling as it does so.
In addition to its latest applications, the ultracold hydrogen created at LCLS-II is a scientific curiosity in itself.
“At 2.0 kelvins, helium becomes a superfluid, called helium II, which has extraordinary properties,” Fauve said. For example, it conducts heat hundreds of times more efficiently than copper and has such a low viscosity, or resistance to flow, that it cannot be measured, he added.
For LCLS-II, 2 Kelvin is the lowest temperatures are expected to reach.
“Lower temperatures can be achieved with very specialized cooling systems that can reach a fraction of a degree above absolute zero, where all motion stops,” Burrill said.
But this particular laser doesn’t have the ability to go to those extremes, he said.
Originally published on Live Science.
