Design and performance of a magnetic spectrometer for antimatter search in space

The conceptual design of the spectrometer and the scientific goals of the AMS experiment, are presented here as well as the measured performances for minimum ionising particles using ground level cosmic-rays and reconstructed events from space. The first results of a test done with relativistic carbon ions at GSI (Darmstadt) are also given, A preliminary version of the AMS apparatus flew on June 1998 on shuttle mission STS-91. In 2002 the complete system will be installed on the space station Alpha and it will take data for three years.