ICARUS: An Innovative Large LAR Detector for Neutrino Physics

ICARUS is an international project that foresees the installation of very large LAr detectors inside the Gran Sasso underground laboratory in order to be sensitive to rare phenomena of particle physics. The detection technique is based on the collection of electrons produced by particle interactions in LAr by a matrix of thousands of thin wires. At the moment the project foresees the installation of a 600,000‐kg vessel (T600). The total amount of LAr can be expanded in a modular way to masses of the order of 10⁶ kg. The T600 houses two identical 300,000‐kg Ar sub‐cryostats that are aluminum boxes about 20‐m long, 4‐m high and 4‐m wide. Safety requirements for the underground installation have led to a unique design for the vessels to prevent LAr spillages even in the case of inner cryostat failure. Electrons must drift over meters requiring the development of special gas and liquid Ar purification units to provide an extremely high LAr purity (better then 0.1 ppb). The cooling system has been designed to assure a high thermal uniformity in the detector volume (less than 1‐K differential). The cryogenic system associated with the final ICARUS configuration is based on three N₂ refrigerators, three 30‐m³ tanks and pump driven two‐phase N₂ forced‐flow cooling of the various sub‐systems. The T600 was successfully tested in Pavia in 2001 and it is now under installation in Gran Sasso for final operation. The future mass expansion strategy is under investigation.