A control and monitor system for the liquid argon cryogenics of the calorimeter of the ATLAS detector

In a few weeks the Large Hadron Collider which is built at CERN will deliver its first beam. ATLAS (A Toroidal Large hadron collider ApparatuS [1]) is one of the four experiments whose aim is to analyze the products of the collisions. As many of these particle detectors, ATLAS is designed with four concentric layers which are, from inside to outside: the inner detector to measure the charged particles tracks, the electromagnetic calorimeter to measure the energy deposited by both electrons and photons, then the hadronic calorimeter and finally the muon detector. The active part of the electromagnetic calorimeter is a bath of liquid argon [2] whose large volume (78 m3) has to be maintained precisely at its operating temperature (about 88 K) by the means of nitrogen circulation. In this paper we will describe how with industry-like control systems an application has been built for the command and the monitoring of the whole cryogenics equipment.