CO2 cooling experience (LHCb)

The thermal control system of the LHCb Vertex LOcator (VELO) is a two-phase CO 2 cooling system based on the 2-Phase Accumulator Controlled Loop (2PACL) method. Liquid carbon dioxide is mechanically pumped in a closed loop, chilled by a water-cooled freon chiller and evaporated in the VELO detector. The main goal of the system is the permanent cooling of the VELO silicon sensors and of the heat producing front-end electronics inside a vacuum environment. This paper describes the design and the performance of the system. First results obtained during commissioning are also presented.