The back-end of the ATLAS detector control system

The ATLAS experiment is one of the experiments at the Large Hadron Collider (LHC), constructed to study elementary particle interactions in collisions of high-energy proton beams. The individual detector components as well as the common experimental infrastructure are supervised by the Detector Control System (DCS). The DCS enables equipment supervision using operator commands, reads, processes and archives the operational parameters of the detector, allows for error recognition and handling, manages the communication with external control systems, and provides a synchronization mechanism with the physics data acquisition system. Due to the enormous size and complexity of ATLAS, the DCS back-end is organized as a hierarchy of finite state machines, allowing for the homogenous control of the whole detector by a single operator. Special emphasis was put on the use of standardized hardware and software components enabling efficient development and long-term maintainability of the DCS over the lifetime of the experiment. Currently, the DCS is being used successfully during the startup phase of the LHC.