G. unel (UNIVERSITY OF CALIFORNIA AT IRVINE AND CERN)
The 40 MHz collision rate at the LHC produces ~25 interactions per bunch crossing within the ATLAS detector, resulting in terabytes of data per second to be handled by the detector electronics and the trigger and DAQ system. A Level 1 trigger system based on custom designed and built electronics will reduce the event rate to 100 kHz. The DAQ system is responsible for the readout of the detector specific electronics via 1600 point to point links hosted by Readout Subsystems, the collection and provision of ''Region of Interest data'' to the Level 2 trigger, the building of events accepted by the Level 2 trigger and their subsequent input to the Event Filter system where they are subject to further selection criteria. Also the DAQ provides the functionality for the configuration, control, information exchange and monitoring of the whole ATLAS detector. The baseline ATLAS DAQ architecture and its implementation will be introduced. In this implementation, the configuration, control, information exchange and monitoring functionalities are provided with CORBA; the control aspects are handled by an expert system based on CLIPS and the data connection between 150 Readout Subsystems, up to 500 Level 2 Processing Units and to 80 Event building nodes is done Gigabit Ethernet network technology. The experience from using the DAQ system in a combined test beam environment where all ATLAS subdetectors are participating will be presented. The current performances of some DAQ components as measured in the laboratory environment will be summarized. Some results from the large scale functionality tests, on a system of a 300 nodes, aimed at understanding the scalability of the current implementation will also be shown.