An introduction to…Helium dewars


From cutting and welding to electronics, aerospace and deep-sea diving to party balloons, helium has a wealth of applications in both gaseous and liquid form.

It is in the latter, its liquid form, that helium is used in perhaps its most renowned application – magnetic resonance imaging (MRI). Liquid helium cools superconductive magnets used in MRI scanners for medical diagnostics, and nuclear magnetic resonance (NMR) laboratory instrumentation. It does so as the only cryogen able to successfully – and safely – achieve the supercool temperatures required.

But with a temperature of -269°C, liquid helium can be more difficult to successfully store than other cryogenic liquids. For many cryogenic instruments, helium consumption is characterised by low daily boil-off and occasional significant large boil-off due to periodic transfers from storage dewars to cryogenic systems. Liquid helium therefore needs considerable expertise in insulation technology to minimise losses, presenting challenges in both transfer technology and helium storage.
Helium storage tanks have to be designed to strict specifications and built to high quality standards due to the physical characteristics of helium, often with liquid nitrogen used to shield the helium in these tanks as a more enduring and cost-effective alternative to using part of the stored helium itself. Liquid helium cryostats are another product in the spectrum of helium storage technologies, often developed for the storage of supercritical helium in various applications. The main advantage of these complex storage facilities lies in the larger payload capacity compared with gaseous storage.

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