The purpose of the LHCb experiment on the main ring at CERN is to study a type of particle called a b quark to gain insights into the small asymmetries between matter and antimatter. Leti, which had previously supplied micro-coolers for CERN's NA62 experiment, was once again selected by CERN to supply the micro-coolers needed to enhance this new world-class experiment.
The particle detectors are much closer to the beam than in the previous configuration, and the circuits' operating frequency is much higher. The micro-coolers will have to maintain the temperature at -20 °C and operate for ten years under vacuum and high radiation.
Leti's microfluidic circuit is made of a network of microchannels just tens of microns deep produced using a plasma etching process on 200 mm silicon wafers. Molecular bonding was used to join a second wafer to the first. The bond had to be defect-free over the entire surface of the wafers to prevent leakage and short circuits. The circuit contains liquid CO2 that evaporates, keeping the system at the target operating temperature. Titanium-nickel-gold contacts were developed to connect the capillaries that provide the cooling fluid.
Prototypes of the cooling circuit were delivered to CERN, and initial cycling tests under operating pressures and temperatures were completed. The first micro-coolers for the experiment are currently being assembled.