The STAR Experiment's Data Acquisition System

STAR is one of the major experiments at the Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory, Upton, USA. RHIC together with STAR began commissioning in June 1999 while the first physics data will be gathered after October 1999. STAR will study ultrarelativistic heavy-ion collisions using its large TPC (Time Projection Chamber) in the first months of running. STAR'S Data Acquisition system is a custom-built massively parallel system hierarchically organized into VME crates interconnected via a fast SCI network. The twelve Sector VME Crates each contain a Sector Broker CPU and twelve custom Receiver Boards, which are connected to the detector via a fiber optic link. Bach Receiver Board hosts three custom Mezzanine Boards with a single Intel 1960HD CPU used to preprocess the data. The system is designed to process 100 events/s of incoming data keeping the output data rate on the order of 20 MB/s (1 event/s). Events will be selected using a third-level trigger utilizing real-time tracking. Buill events arc transported via SCSI to a workstation acting as an event buffer and forwarded to the RHIC Computing Facility via Gigabit Ethernet for final archiving.