The design and operation of the detector control system of the ALICE experiment at CERN

The control systems developed for large high energy physics experiments usually do not have strict real time constraints. On the other hand, the correct functionality of detector electronics cannot be achieved without a reliable control system. Different architecture and operational principles of fast front-end electronic modules and complex SCADA systems create a challenge for overall design and integration. In the presentation we describe the Detector Control System of ALICE one of the 4 LHC experiments at CERN. Eighteen sub-detectors based on different technologies, control architectures and operational requirements need to be integrated into a coherent system allowing for centralized operation. We describe the strategy used in ALICE with focus on the operation of front-end electronics. A standardized software abstraction level allows for unified operation of modules, hiding the complexity of the underlying hardware architecture and represents the different front-ends as devices reacting to the same set of commands. We describe the software implementation of this approach and its integration into the central system. On vertical slices of the system we explain the implementation principles covering the full chain from the configuration database to device registers. The read-back data carries information on the device status and conditions. It provides feedback to the operators as well as to the monitoring and data analysis software. We explain how the data flow is organized in ALICE and how it is used to allow for operation of millions of readout channels by a single operator in a smooth and efficient way.