The Proximity Cryogenic System for the ATLAS Toroidal Magnets

ATLAS is a very high-energy detector for the Large Hadron Collider (LHC) at CERN. The superconducting magnet used to provide the required magnetic field consists of four sub-systems: a central solenoid and a very large toroidal magnet comprising two end-cap magnets and the barrel toroid magnet. The associated cryogenic system, currently in the final specification and procurement phase has been sub-divided into three parts: internal, proximity and external. The internal cryogenics minimizes and extracts the heat loads to/from the 4.5 K cold mass and its thermal shields, while the proximity cryogenics takes the cooling capacity generated by the external common system and distributes it to the four magnets according to the various operating scenarios. Two independent proximity cryogenic systems have been designed taking into account the difference in cooling principle of the solenoid and the three toroids, respectively.