Cryogenic Design and Operation of a Liquid Argon Photon / Hadron Calorimeter at Fermilab

Abstract

A Liquid Argon Calorimeter (LAC) was designed for and has operated in a high energy physics experiment, as part of Fermilab’s fixed target physics program. The LAC measures the position and energy of photons / electrons and hadrons. The calorimeter consists of a photon detector (~22 tons) and a hadron detector (~150 tons). The detector segments are suspended from large I-beams into a liquid argon vessel. The foam insulated vessel has a capacity of ~70,000 liters of liquid argon, which is the ionization media for the experiment. A gantry allows for the lateral movement of the detector. During calibration, the detector is swept laterally through the beam for a distance of 4m. The vessel can also be emptied and then moved out of the beamline over a pit to allow the lowering of the bottom part of the vessel and access to the detector. The pressure of the liquid argon is controlled by a liquid nitrogen cooling coil. The LAC was operated successfully through one 6-month running period, which started in September of 1987 and has remained cold and full since then. The assembly, cooldown, unmanned operations and special considerations such as liquid argon purity are described.