AMS-02 Experiment

AMS-02 The Alpha Magnetic Spectrometer on the International Space Station

AMS-02 is a state-of-the-art particle physics detector, designed to operate as an external module on the International Space Station (ISS). It uses the unique environment of space to study the universe and its origin by searching for antimatter and dark matter while performing precision measurements of cosmic rays composition and flux.

The instrument was launched by the Space Shuttle Endeavour (STS-134) to the ISS on 16- May-2011, installed on the upper Payload Attach Point on 19-May-2011, and will operate on the ISS for the lifetime of it. The detector consists of a permanent magnet and nine planes of silicon tracker measuring the momentum p, charge Z and rigidity R=p/Z of charged cosmic rays, four planes of time-of-flight counters, a transition radiation detector (TRD), a ring imaging Čerenkov detector (RICH), an electromagnetic calorimeter (ECAL), and an array of 16 anticoincidence counters. It operates continuously on the ISS and is monitored and controlled continuously from the ground.

AMS-02 has measured over 140 billion cosmic rays up to now, investigating the details of the cosmic ray spectra. In the following, a selection of the latest and most significant AMS measurements.

Electron and positron spectra: AMS measured in detail the lepton component of cosmic rays, reporting the electron and positron differential fluxes [Ref.1,2] measured between 0.5 GeV and, respectively, 1.4 TeV and 1 TeV. Data show a different behaviour of the cosmic-ray electrons and positrons, indicating that most high energy electrons originate from different sources than high energy positrons.

Primary and secondary cosmic rays: AMS measured differential fluxes for primary (He, C, O) and secondary nuclei (Li, Be, B) cosmic rays, as well as Nitrogen [Ref.3], which has both primary and secondary components.

Protons, Helium fluxes, Helium isotopes and time dependent measurements: AMS also performed precise measurements of protons and Helium, the most abundant components of cosmic rays. In particular, thanks to its long exposure and the high collected statistics, AMS is monitoring in time the galactic cosmic ray flux and following its temporal variation in connection with solar activity. It has already measured the differential flux temporal evolution for several species – protons, Helium, electrons and positrons – during the maximum of solar cycle 24 towards the current minimum [Ref. 4,5]. Moreover, the most recent AMS results report 3He and 4He fluxes as detected over the course of six years [Ref.6], providing for the first time the measurement of the rigidity dependence of the 3He/4He flux ratio up to 15 GV. At low energy, the two isotopes exhibit nearly identical variations with time due to solar modulation, with a significant long-term time dependence in the 3He/4He ratio below 4 GV.

More information about the mission is available at

The complete AMS-02 dataset is available for download at