Design and implementation of the ATLAS detector control system

The overall dimensions of the ATLAS experiment and its harsh environment, due to radiation and magnetic field, represent new challenges for the implementation of the detector control system (DCS). It supervises all hardware of the ATLAS detector, monitors the infrastructure of the experiment, and provides information exchange with the LHC accelerator. The system must allow for the operation of the different ATLAS subdetectors in stand-alone mode, as required for calibration and debugging, as well as the coherent and integrated operation of all subdetectors for physics datataking. For this reason, the detector control system is logically arranged to map the hierarchical organization of the ATLAS detector. Special requirements are placed onto the ATLAS detector control system because of the large number of distributed I/O channels and of the inaccessibility of the equipment during operation. Standardization is a crucial issue for the design and implementation of the control system because of the large variety of equipment and the high number of different groups involved working all around the world. The functions of the two main components of the DCS, namely the distributed back-end software system, which will be based on a commercial SCADA package, and the subdetector's front-end systems, with extensive use of the CAN fieldbus, are explained. The standard readout chain of the DCS, which comprises both back-end software and general-purpose front-end equipment, is described and its performance is discussed.