A British firm claims to have found a way to help medical and physics researchers reduce their reliance on increasingly expensive helium.
Lab equipment that uses superconducting magnets, such as MRI scanners and certain spectrometers, typically requires cooling systems based on liquid supplies of helium, an increasingly limited resource that has experienced volatile price fluctuations in recent years.
London-based Cryogenic Ltd says it has adapted existing technology to replace the liquid helium element with a mechanical refrigeration unit that directly reduces the magnet’s temperature to near absolute zero by conducting the unit’s cooling power to a cryostat vessel.
Cryogenic’s magnet consultant, Jonathan Cole, said the technology could help end researchers’ dependence on the market for helium, which is manufactured as a byproduct of natural gas, to operate their equipment.
‘When gas fields are closed down for maintenance, for example, we’ll see a temporary shortage of helium for several months and the price will go up, and all the hospitals using helium will correspondingly be paying more,’ he told The Engineer. ‘Most of the predictions are that slowly the price will go up and up.’
Superconducting magnets in machines such as nuclear magnetic resonance (NMR) and electron spin resonance (ESR) spectrometers, which are used to study materials, must be cooled to temperatures of around 3.5K (-270ºC).
Conventional “wet” cooling systems involve immersing the magnet in a continuous supply of liquid helium, which is gradually boiled off and must be regularly replaced.
Cryogenic has instead adapted a cryocooler, which uses a finite amount of helium gas that is continually compressed and expanded as a heat exchange medium, designing the conduction system and shielding to maximise efficiency and provide enough cooling power to reach the required temperature.
‘The boiling point of helium is 4.2K and it turns out that the cryocoolers will go below 3K,’ said Cryogenic’s managing director, Jeremy Good. ‘A lot of people were sceptical and perhaps quite a few still are that it can work without liquid but the answer is they’re wrong.’
Some laboratories already use cryocoolers to recondense their liquid helium so they don’t need to keep buying new supplies of helium, although this means the helium must be cleaned of air.
‘We are developing a solution that will hopefully be cheaper than the production method because we are reliquefying,’ said Southampton University’s professor of cryogenics, Yifeng Yang.
He said the potential issue with connecting a cryocooler directly to an NMR spectrometer would be compensating for the vibrations the cooling unity produced. ‘[But] it’s highly possible. From our point of view it depends on how much it will cost … I would like to see the details.’
Cryogenic says its “dry” system would also avoid problems associated with “quenching”, where part of the magnet suddenly stops superconducting and begins generating large amounts of heat, rapidly boiling off the liquid helium and requiring large systems to evacuate the resulting gas.