The COMPASS spectrometer at CERN

The COMPASS spectrometer was designed for the NA58 fixed-target experiment at the CERN SPS. The physics aim is the study of the spin structure of the nucleon and the spectroscopy of hadrons with muon and hadron beams. Several novel techniques like Micromegas, GEMs and straw tracking detectors were deployed as well as large area CsI- based photo detectors for the RICH. A powerful DAQ and custom front- end electronics allow very high data rates. The paper focuses on the performance of the spectrometer during the first physics run in 2002 in which 5 billion events corresponding to 260 TByte of data were collected with a 160 GeV muon beam and polarised deuteron target.