Abstract
In the ATLAS experiment at the LHC, the output of read-out hardware specific to each subdetector will be transmitted to buffers, located on custom made PCI cards (ROBINs). The data consist of fragments of events accepted by the first-level trigger at a maximum rate of 100 kHz. Groups of four ROBINs will be hosted in about 150 Read-Out Subsystem (ROS) PCs. Event data are forwarded on request via Gigabit Ethernet links and switches to the second-level trigger or to the Event builder. In this paper a discussion of the functionality and real-time properties of the ROS is combined with a presentation of measurement and modelling results for a testbed with a size of about 20% of the final DAQ system. Experimental results on strategies for optimizing the system performance, such as utilization of different network architectures and network transfer protocols, are presented for the testbed, together with extrapolations to the full system.
Highlights
THE ATLAS experiment is one of the four large experiments aimed at studying high-energy particle interactions at the Large Hadron Collider (LHC)
The RoI rates for each possible RoI location and type are obtained with a straightforward calculation. Inputs for it are: the LVL1 accept rate, exclusive fractional rates for the various LVL1 trigger menu items, the number and type of RoIs associated with each trigger item and the - area associated with the RoI location and type
The rates of requests received by each Read-Out Subsystem (ROS) PC and the request rates for each ROL are obtained using the mapping of the detector onto the ROLs, the acceptance factors of the various LVL2 trigger steps, and the RoI rates for the RoI locations associated with the - areas from which data are requested (RoI type and detector dependent)
Summary
THE ATLAS experiment is one of the four large experiments aimed at studying high-energy particle interactions at the Large Hadron Collider (LHC). The LHC is under construction at the European Laboratory for Particle Physics CERN in Geneva and is scheduled to come into operation in the year 2007. At present the ATLAS experiment [1] is being installed in its underground cavern and the commissioning process has started. The design of the HighLevel Trigger and Data-Acquisition (TDAQ) system has been documented in [2]. This paper concentrates on the flow of data in the system [3] and reports on the implementation of the Read-Out Subsystem (ROS) and on results of recent testbed and modeling studies of the TDAQ system
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