Helium is a limited resource; it is rare and one of the few elements so light that it can escape the Earth's atmosphere. It is also has the lowest boiling point of any element, at -269°C, just a few degrees above the coldest possible temperature, absolute zero (-273°C).
This makes it of key importance for many low temperature experiments at ISIS, as well as the superconducting magnets used in MRI scanners, which must be cooled to extremely low temperatures to generate the hugely powerful magnetic fields required.
With two thirds of ISIS experiments using liquid helium, the demand for low temperature experiments at ISIS increasing and growing concerns over the limited supply of helium, a project began to develop a helium recovery facility on site. The aim was to reduce the amount of helium that was purchased by capturing, compressing and storing helium, before making it available for re-use.
The facility opened in 2015, with 2 kilometres of pipework connecting the outlets from the cooling systems on the instruments and targets to a large balloon in the new helium recovery facility. This then could be recycled to supply both ISIS target stations with helium gas and returned to the supplier for liquefaction.
Once the gas recycling system was installed, the team bought a liquefier second-hand, which was added into the system. This brought in extra capacity to the storage system, as liquid helium is much denser than the gas. Their thirty 120 litre helium dewars and five 250 litre dewars can hold up to 4850 litres, which would be over 3.5 million litres if it was stored as a gas.
The combination of liquid helium, gaseous helium in the balloon and compressed helium in the tanks means that the whole system is a complex balancing act. The team has had to expand to cope with this, and now has two full time staff members managing the facility.
The goal is for the facility to become self-sufficient, recycling all of the helium used. At the moment, they are close to 90%, and finding small ways to improve pipework and collection to get this as high as possible.
Before they reach an optimum recovery level, they are still relying on external suppliers, which can be unpredictable if global helium supply is low, or if there is a global pandemic! To reduce the impact of this uncertain supply, they have recently installed a new collection of multi cylinder packs (MCPs) that hold gas cylinders, bringing even more capacity into the system. They now have 40 MCPs in total, which each hold 800 litres of helium at 200Bar. This is the same as 6.4 million litres of helium gas, or over 1.5 million party balloons.
Their system has been a huge success; despite the increase in helium needed for experiments at ISIS over the last few years, the amount of helium lost by ISIS has reduced by over 80% since the facility opened. That means that over 35,000 litres of liquid helium, or 26 million litres of gas, is recycled every year.
Richard Down, ISIS Cryogenic Team Leader, explains; “The ISIS Helium recovery project was removed in the early 1990's due to the costs of renewing an aging system, and the lack of a suitable workforce. 30 years have passed and, due to Helium shortages and increasing costs, we were given the opportunity to develop an infrastructure to recover this incredible resource that will last for many years to come".
The next step is to support the other facilities on campus: a 600 metre-long pipe from Diamond Light Source has been commissioned to enable the helium recovered from Diamond to be recycled in the ISIS facility. The project continues to work towards a sustainable system that will allow low temperature experiments to continue long into the future.