The AMS-02 TRD for the International Space Station

Abstract

The Alpha Magnetic Spectrometer (AMS-02) is an experiment which will be mounted on the international space station (ISS) to measure primary cosmic ray spectra in space. A key element is a transition radiation detector (TRD) to distinguish an e/sup +/ or p/sup -/ signal reducing the p/sup +/ or e/sup -/ background by a rejection factor 10/sup 2/ - 10/sup 3/ in an energy range from 10 to 300 GeV. This will be used in conjunction with an electromagnetic calorimeter to provide overall p/sup +/ rejection of 10/sup 6/ at 90% e/sup +/ efficiency. The detector consists of 20 layers of 6 mm diameter straw tubes alternating with 23 mm layers of polyethylene/polypropylene fleece radiator. The tubes are filled with an 80%:20% mixture of Xe : CO/sub 2/ at 1.2 bar absolute from a recirculating gas system designed to operate >3 years in space. The layers are mounted to 0.2 mm precision in a stable carbon fiber composite/aluminum honeycomb octagonal mechanical support. There are in total 5248 straw tubes which are read out by a custom-made DAQ system in less than 70 /spl mu/s. The electronics must be low in power consumption and sustain the stringent requirements of operation in space. The construction of the detector and its electronics is presented in this paper.