R744 Primary Ultra-Low temperature Project for ATLAS & CMS Detectors Phase-2 Cooling Upgrade

In 2018, the CERN, ATLAS and CMS experiments decided that the cooling systems for the thermal management of the future phase-II silicon detectors will share the same design entirely based on CO2 refrigeration technology. The cooling systems will be based on CO2 vapour compression booster, composed of a two compressor stages with transcritical R744 equipment and of a low-temperature secondary CO2 pumped loop. This presentation focuses on the solution adopted for the R744 Primary part led by the EN-CV group while the secondary CO2 pumped loop being managed by the EP-DT group. It also introduces the project’s roadmap, describing the key milestones and its technical, safety and regulatory challenges with regards to the use of this natural and environmentally friendly refrigerant.