A particle accelerator fusing electrons here on Earth has reached temperatures colder than those in space.
The habits x-ray free-electron laser at the Department of Energy’s SLAC National Accelerator Laboratory — part of an upgrade project to the Linac Coherent Light Source (LCLS), 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 movement stops. That icy environment is crucial for the accelerator, because at such low temperatures the machine becomes superconducting, meaning it can propel electrons through it with virtually zero energy loss.
Even empty regions of space are not that cold, because they are still filled with the cosmic microwave background radiation, a remnant of shortly after the big bang that has a uniform temperature of minus 454 F (minus 271 C), or 3 K.
“The next-generation superconducting accelerator of the LCLS-II X-ray-free electron laser has reached its operating temperature of 2 degrees above absolute zero,” Andrew Burrill, director of the SLAC’s Accelerator Directorate, told Live Science.
LCLS-II is now ready to accelerate electrons at 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, meaning we sent more X-rays to users in a matter of hours. [who aim to utilize them in experiments] than LCLS has done in the past 10 years,” said Burrill.
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 its predecessor. This should help researchers examine complex materials in unprecedented detail. The high-intensity, high-frequency laser pulses enable researchers to see with unprecedented clarity how electrons and atoms in materials interact. This will have a number of applications, from helping to reveal “how natural and man-made molecular systems convert sunlight into fuels, and thus how to control these processes, to understanding the fundamental properties of materials that enable quantum computing” said Burill. †
Related: 10 cosmic mysteries the Large Hadron Collider was able to unravel
Creating the frigid climates in the throttle took some work. For example, to keep the helium from boiling away, the team needed super-low pressures.
Eric Fauve, director of the Cryogenic Division at SLAC, 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 water boils at 250°F (121C), while the reverse is true at altitude, where the pressure is lower and water boils at a lower temperature
“It’s pretty much the same for helium. However, at atmospheric pressure, helium boils at 4.2 kelvins; this temperature will decrease as the pressure decreases,” Fauve said. “To bring the temperature down to 2.0 Kelvin, we need a pressure as low as 1/30 the atmospheric pressure.”
To achieve these low pressures, the team uses five cryogenic centrifugal compressors, which compress the helium to cool it, then expand it in a chamber to lower the pressure, making it one of the few places on the planet. Soil where 2.0 K helium can be produced on a large scale.
Fauve explained that any cold compressor is a centrifugal machine equipped with a rotor/impeller similar to that of an engine’s turbocharger.
“As it spins, the impeller accelerates the helium molecules and creates a vacuum in the center of the wheel where molecules are sucked in, creating pressure at the edge of the wheel where molecules are ejected,” he said.
Compression forces the helium to assume its liquid state, but the helium escapes into this vacuum, where it quickly expands as it cools.
In addition to the ultimate applications, the ultra-cold 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 it has such a low viscosity — or resistance to flow — that it can’t be measured, he added.
For LCLS-II, 2 Kelvin is as low as expected.
“Lower temperatures can be achieved with highly specialized cooling systems that can reach a fraction of a degree above absolute zero, stopping all movement,” Burrill said.
But this particular laser doesn’t have the ability to reach those extremes, he said.
Originally published on Live Science.