One of the world’s most sophisticated scientific facilities is turning to ultra-low temperatures to try and unravel hidden secrets of our Universe. It’s one of the most famous scientific installations in the world – and it’s getting a cool upgrade.
Physicists use the Large Hadron Collider (LHC), buried in the ground on the border between France and Switzerland, to unravel secrets of the tiny particles that make up our Universe. The LHC works by smashing some of these particles into one another and observing what happens when they collide.
By the 2030s, the LHC – built by the European Organization for Nuclear Research (Cern) – will produce many more of these collisions. The idea is to obtain even more precise measurements of the subatomic particles that result in those impacts. Should any measurements ever deviate from values defined by the so-called Standard Model of physics, then, “we’ll know there must be some new physics,” says Martin Aleksa, technical coordinator of the Atlas experiment at Cern.
But, surprisingly, this pioneering research probing the intricacies of matter itself depends, at least in part, on technology that is also used in supermarket fridges. Low temperatures are prized by many scientists. Chilly experiments can slow subatomic particles down or stabilise materials in such a way that makes them easier to study.
Heat Exchangers and Carbon Dioxide Cooling
Stefan Brohm, lead business engineer at Swep, a manufacturer of heat exchangers explains, “We want to be one of the technology leaders with this heat exchanger so we started developing it together with Cern.” Different kinds of heat exchanger are used in fridges, heat pumps, cars and even aircraft engines to transfer heat around.
Swep’s heat exchangers will help to cool down parts of the LHC’s Atlas experiment to -45C (-49F) in an effort to reduce electronics noise associated with radiation. The specific heat exchanger Swep developed for the LHC upgrade allows for the use of carbon dioxide as a refrigerant. Although a greenhouse gas, carbon dioxide is much less potent than the refrigerant used in the previous system.
The Coldest Places on Earth
Other parts of the LHC require much lower temperatures than Atlas – these regions of the collider are among the coldest places on Earth. For instance, more than 1,000 electromagnets dotted around the installation are cooled to a jaw-dropping low of 1.9 Kelvin (-271C/-456F).
Below 10 Kelvin (-263C/-441F), the niobium-titanium wire coils at the heart of the LHC’s electromagnets become superconductors – meaning they allow electricity to pass through them with no resistance. This ensures they do not overheat.
Achieving such temperatures takes weeks and relies on gradually cooling liquid helium down in various stages until it reaches that target temperature of 1.9 Kelvin. That’s colder than even the Boomerang Nebula, the coldest known natural place in the Universe.
Dilution Refrigeration and Helium Isotopes
One key technology scientists use to reach super low temperatures is called dilution refrigeration. It uses two helium isotopes: helium-4 and helium-3. Helium-4 is used in party balloons while helium-3 is one of the most expensive substances in the world. Its price fluctuates but a litre of the stuff can cost thousands of pounds, says Richard Haley, professor of low temperature physics at Lancaster University.
Low temperatures cause helium-3 to mostly separate from and float on top of helium-4, a bit like oil on water. When some helium-3 atoms are then pumped downwards into the region of mostly helium-4 atoms below them, they absorb heat in the process, which has a profound cooling effect.
Unlike your coffee, dilution refrigeration can reach incredibly low temperatures, even down to 5-10 millikelvin. Ultra-low temperature physics is a “frontier field,” says Haley. “If you cool something down to a temperature it’s never been at before, it might do something interesting.”
Scientists have even used low temperatures to slow down light from its usual speed of 1.08 billion km/h to just 61 km/h – where it would lag far behind cars travelling at the speed limit on a British motorway.
Applications Beyond Physics
Some scientists use ultra-low temperature setups to study how the Universe might have behaved in the aftermath of the Big Bang. And dilution fridges are crucial for quantum computers, too. The large, golden chandelier-like devices you sometimes see in pictures of quantum computers are the dilution fridges that make quantum computing possible. The super low temperatures are necessary because heat causes errors in quantum bits, or qubits.
There are other engineering applications. Computer chips have become smaller and smaller over the years but that means imaging them has become harder. It’s possible to cool down semiconductors to as low as three Kelvin in order to take sharp pictures of them for analysis or quality control purposes.
“You’re looking at a small area but if it’s warm and expanding or contracting, even a little bit, it won’t give you as clear as image,” says Dylan Cawman, sales engineer at Advanced Research Systems, a company that makes cryogenic cooling equipment for a range of applications.