Results of a high intensity test beam with a large number of GEM+MSGC detector modules

A system of 18 detector modules, designed for the use in the forward-backward tracker of the CMS experiment, has been tested in a high intensity pion beam at the Paul-Scherrer-Institut (PSI, Villigen, CH). Each module was equipped with four Micro Strip Gas Counter (MSGC) substrates and a large area Gas Electron Multiplier (GEM) as second amplification stage. The robustness of the detector modules when operated within an LHC-like environment was studied. Voltage settings yielding 98% detection-efficiency for minimum ionising particles were set, and the number of strips lost over a period of two weeks under permanent irradiation with a particle flux of ~4*10/sup 3/ Hz/mm/sup 2 / was recorded. The corresponding loss of strips was well below 10% of the total number of channels read out. A maximum signal-to-noise ratio of 100 has been achieved.