The Cryogenic System for the ATLAS Liquid Argon Detector

The ATLAS experiment will include three argon detectors of unprecedented size. The total liquid argon fill of the three cryostats is 83 m3. Gas bubble formation which is detrimental for the functioning of the detector is avoided by sub-cooling of the liquid argon volume with saturated liquid nitrogen heat exchangers placed in the cryostats. Furthermore, to prevent degradation of the detector performance, the maximum temperature gradient across the total liquid volume must be kept within 0.6 K. Additional severe constraints are imposed by the request of uninterrupted cryogenic operation during several years and by the safe handling of a large amount of argon in a 100 m deep underground area.