The ams-02 transition radiation detector for the international space station

ne Alpha Magnetic Spectrometer (AMS-02) is a large experiment in the International Space Station (ISS) intended to measure primary cosmic ray spectra in space. It sits outside of the station, looking out into space. High-energy particles pass through it, interacting with different detectors on the way. The Transition Radiation Detector (TRD) contributes to distinguish an e(+) or p(-) signal reducing the p or e(-) background by a rejection factor 102 to 103 in the energy range from 10 to 300 GeV. This detector will be used in conjunction with an electromagnetic calorimeter to provide an overall p rejection of 106 with 90% efficiency for positrons. AMS-02 TRD consists of 20 layers of straw proportional tubes alternating with layer of fiber fleece radiator. The layers are mounted in a stable and light carbon fiber composite/aluminum honeycomb octagonal support, fixed by an M-structure to the AMS-02 magnet flange. A space qualified redundant electronic subsystem processes signals coming from the 5248 straw tubes providing front-end readout, first level DAQ and interface to the AMS-02 trigger/DAQ system. The straw tubes are filled with a Xe:CO2 gas mixture provided by a gas circulating system capable to operate more than 3 years in space. The gas control system of the TRD is also an essential item for its performance. To obtain the required discriminating power, a stringent control of gas parameters is necessary. The construction of the detector is presented.