AMS (Alpha Magnetic Spectrometer) experiment

The Alpha Magnetic Spectrometer (AMS) experiment is a large international collaborative program. Taking part in this program are scientists and engineers of 30 odd research institutions from 11 countries and regions like the United States, China, Russia, Finland, Germany, Italy, Romania, Switzerland, etc. AMS is the first large magnetic spectrometer ever sent into the space by human beings. Loaded on board the American space shuttle ST91 of Discoverery on June 2, 1998, it successfully underwent the first 10-day experimental flight in space, 400 km away from the earth. And at the end of 2009, it will be sent to the international space station for 3 years operation. It is the first precise magnetic spectrometer for particle physics experiment carried out in space.

Magnetic spectrometer is a kind of experimental facility extensively used in high-energy physics experiments. The more than 3-ton AMS that has experienced the trial flight comprises the permanent magnet and a set of precise detectors. Its chief components are as follows:

  1. Time of flight counter (composed of scintillators and photomultipliers and used for measuring the flying speed of particles)
  2. Silicon strip tracking detector (used for measuring the particle flying track and determining the momentum of particle, the charge and sign)
  3. Cerenkov counter (used for particle identification, determining the flying direction of particle and further measurement of the particle charge)
  4. Veto counter (repelling recording the events of particles from the sides of AMS)

The above contents constitute the first stage project of AMS, known as AMS – 01. Following the successful flight of AMS and the safe landing on the ground, modifications will be made as follows in the magnetic spectrometer to be sent to the international space station at the end of 2005 based on the experience acquired from the first flight and also for great improvement of the detectors performances and detecting ability:

  1. Permanent magnet replaced by superconducting magnet (to increase the measuring ability of particle momentum)
  2. To increase the layers of silicon strip tracking detector (to improve the measuring ability of particle momentum)
  3. To build more electromagnetic calorimeters (for particle identification and measurement of particle energy
  4. Transit radiation detector (for particle identification)
  5. Cerenkov counter upgraded to Cerenkov ring image detector)

The above-mentioned upgrades constitute the second stage project of AMS, known as AMS-02. The first published results came out in 2013 and 2014, in particular a high precision measurement of the positron over electron spectrum up to 500 GeV. The most recent results are annouced here.