The European Organization for Nuclear Research (CERN) has chosen transcritical CO2 (R744) cooling for the Large Hadron Collider (LHC)’s upgraded tracking detector systems.
This was announced in a scientific paper published in Applied Sciences on August 11. The system has been developed by researchers from CERN, and partners from the Norwegian University of Technology and University of Cape Town in South Africa.
The LHC is the world’s most powerful particle accelerator, a 27-kilometer underground circular tunnel sitting on the border between France and Switzerland. It consists of a ring of super conducting magnets with a number of accelerating structures to boost the energy of the particles on their way round. Detectors then record the results of the collisions between the particles.
“CO2 evaporative cooling systems based on mechanically pumped loops are more and more frequently used for particle trackers, because they allow for the use of smaller tubes (hence reducing the amount of material in the tracking region), while presenting more favorable thermo-physical properties compared to other refrigerants,” the CERN scientists said in the paper.
“However, a conventional R744 chiller system off the shelf would not comply with the particular requirements of both detectors. Therefore, the refrigeration process, the equipment and control logic associated had to be rethought.”
“CO2 evaporative cooling systems based on mechanically pumped loops are more and more frequently used for particle trackers, because they allow for the use of smaller tubes, while presenting more favorable thermo-physical properties compared to other refrigerants”CERN
The new cooling system therefore has a very specific design. The two-stage CO2 primary system, located on the surface, generates cold at -53°C (-63.4°F) for a secondary CO2 pumped loop, which is installed 100meter underground, and rejects the heat created during operation of the LHC.
The system is “capable of evacuating from the detector volume a nominal power up to 300kW for ATLAS and 500kW for CMS, while ensuring a temperature of the refrigerant in the detector heat exchangers down to −43°C (-45.4°F),” the researchers explained.
“The [refrigeration] process must be reliable and remain stable regardless of the amount of heat exchanged, which will amount to hundreds of kilowatts and is expected to vary throughout the lifetime of the detectors,” the researchers said about the system design.
For more information about the design of the CERN CO2 cooling system and technical details of the system, click here.
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