The LHCb Vertex Detector (VELO) is currently being upgraded to a lightweight, capable pixel detector of 40 MHz. The thermal management of the system will be provided by evaporative CO2 circulating in micro channels. This solution has been selected because of the excellent thermal efficiency, the absence of thermal expansion, as well as the ability of CO2 and the contribution to the material budget.
Although micro channel cooling is gaining considerable attention for applications related to microelectronics, it is still a novel technology for particle physics experiments, especially when combined with evaporative CO2 cooling. The LHCb design focusses on an efficient layout of the channels with a fluidic connector and its attachment. The distribution of the coolant is ensured by the use of restrictions implemented before the race.
The microchannel production is a complex process involving the production of quality control and the production of the process. The quality control includes a cyclic stress test in pressure and temperature, high pressure tests with helium, and surface evaluation. The microchannel production is now underway and will be described along with future R & D improvements that could be envisaged.