Stopping the haemorrhage

The cryogenic line, which has been supplying liquid helium to the SM18 Hall area dedicated for tests on radiofrequency cavities and cryomodules for the past 20 years, is currently being dismantled. It will soon be replaced with a state-of-the-art infrastructure with an up to 10 times enhanced performance.


Performing preliminary assembly works on the new cryogenic infrastructure in SM18.

Part of the SM18 Hall is devoted to tests on radiofrequency (RF) cavities and cryomodules used for beam acceleration in various CERN experiments and accelerators. Inserted into cryostats and cooled to cryogenic temperatures, these cavities are tested at extreme conditions, which reflect their operating environment.

The existing cryogenic infrastructure supplying liquid helium to the six RF tests stations – four vertical cryostats and two bunkers for the horizontal cryomodules – hasn’t quite been delivering the goods. Of the 25 g/s of liquid helium that the cryogenic tank was able to supply, only 15 to 17 g/s was actually delivered to the stations. This was due to alarming thermal losses caused by the vaporisation of over 30% of the liquid. “The existing cryogenic line dates back to the beginning of the 1990s,” explains Vladislav Benda, who is in charge of the operation of the cryogenic infrastructure at SM18. “Fortunately, nowadays, there are new design and insulation solutions that make it possible to construct much more efficient cryogenic lines.”

Almost 50 m of line, from the helium tank to the last test station, will be replaced. “The new infrastructure has been designed and is being built at CERN,” explains Olivier Pirotte, who is in charge of the project. “It will consist of a cryogenic line and six service modules, which will supply each of the six test stations.” Vladislav Benda adds: “Thanks to this equipment, I am confident that thermal losses can be reduced by a factor 10.”

In addition to its greater thermal efficiency, the future infrastructure will also have more functionality with the addition of a new option. The six stations can be used to conduct independent tests with superfluid helium (at 1.8 K) and three of them will now be devoted to this. “We are awaiting two new vertical cryostats which have been specially designed for the superfluid helium tests,” points out Pierre Maesen, who is in charge of the RF tests in SM18. “They will enable us to meet the increasing demand for tests at temperatures below 2 K – particularly for the Superconducting Proton Linac (SPL) project and for the development of the ‘Crab’ cavities used for the luminosity upgrade of the LHC.”

For the time being, the teams are continuing to dismantle the existing cryogenic line. The new cryogenic infrastructure should be commissioned next spring.

by Anaïs Schaeffer