THE CONTROL SYSTEM FOR THE CO2 COOLING P LANTS FOR PHYSICS EXPERIMENTS

CO2 cooling has become interesting technology for current and future tracking particle detectors. A key advantage of using CO2 as refrigerant is the high heat transfer capabilities allowing a significant material budget saving, which is a critical element in state of the art detector technologies. Several CO2 cooling stations, with cooling power ranging from 100W to several kW, have been developed at CERN to support detector testing for future LHC detector upgrades. Currently, two CO2 cooling plants for the ATLAS Pixel Insertable B-Layer and the Phase I Upgrade CMS Pixel detector are under construction. This paper describes the control system design and implementation using the UNICOS framework for the PLCs and SCADA. The control philosophy, safety and interlocking standard, user interfaces and additional features are presented. CO2 cooling is characterized by high operation stability and accurate evaporation temperature control over large distances. Implemented split range PID controllers with dynamically calculated limiters, multi-level interlocking and new software tools like CO2 online p-H diagram, jointly enable the cooling to fulfil the key requirements of reliable system.