The helium cryogenic system for the ATLAS experiment

The magnetic configuration of the ATLAS detector is generated by an inner s uperconducting solenoid and three air-core toroids (the barrel and two end- caps), each of them made of eight superconducting coils. Two separated heli um refrigerators will be used to allow cool-down from ambient temperature a nd steady-state operation at 4.5 K of all the magnets having a total cold m ass of about 600 tons. In comparison with the preliminary design, the heliu m distribution scheme and interface with the magnet sub-systems are simplif ied, resulting in a considerable improvement of the operational easiness an d the overall reliability of the system at some expense of the operational flexibility. The paper presents the cryogenic layout and the basic principl es for magnets cool-down, steady state operation and thermal recovery after a fast energy dump.