A large size MICROMEGAS detector for the COMPASS experiment at CERN

We have developed and built 12 planes of large-size (40/spl times/40 cm/sup 2/) MICROMEGAS detectors. These detectors were installed at CERN and successfully operated during the first year of the COMPASS data taking. All important detector parameters: space and time resolutions, discharge probabilities, noise figure and experimental efficiencies were found to agree with the design values.