The Performance of the AMS-02 Trd

The Alpha Magnetic Spectrometer (AMS-02) is an experiment which will be mounted on the International Space Station (ISS) in 2007 to measure primary cosmic ray spectra in space and to perrform an indirect search for dark matter in the universe. To this aim, AMS includes a Transition Radiation Detector (TRD) to be able to distinguish an e+ or psignal, reducing the p+/ebackground by a rejection factor 10.' in the energy range 10-300 GeV. The TRD will be used in conjuction with an electromagnetic calorimeter to provide overall p+ rejection of at 90% e+ efficiency. A TRD prototype has been calibrated and its performance measured in test beams with p', e', F-, 71from 3 to 250 GeV/c and compared with Montecarlo predictions. It achieved a rejection factor ranging from 2000 to 140 for protons with energy varying from 15 to 250 GeV. The TRD Modules and structures have undergone an extensive program of space qualification. Selected Modules have undergone a long term test in a vacuum chamber. TRD flight version is under construction, and so far within specifications and schedule