The RPC level-1 muon trigger of the ATLAS experiment at the LHC

The three-level ATLAS trigger system has been designed to reduce the initial LHC interactions rate from 1 GHz, to ~100 Hz in order to allow permanent data storage. This result must be achieved preserving the less probable physics signals against a large background therefore providing a challenge task for the trigger and DAQ system. The level-1 muon trigger in the barrel region of the muon spectrometer is provided by resistive plate chambers (RPC) working in avalanche mode. More than 1000 RPC units of different sizes will he installed covering a surface of about 3650 m² with a 350000 readout channels. A detailed simulation of the level-1 has been developed in order to optimize the trigger logic design and to study its performances. A description of the level-1 trigger in the barrel and preliminary results of its performances are presented.