The Alpha Magnetic Spectrometer, developed by an international collaboration lead by the Nobel Prize Samuel Ting, is the first large acceptance (about 0.5 m2 sr) particle detector designed to operate in space to measure, for many years, cosmic ray fluxes. The second version, AMS-02, was installed on 19 May 2011 on board of the International Space Station (ISS) Alpha, which is flying in a low (about 400 km) orbit around Earth, where it will acquire data for several years (NASA AMS web page).
In its first configuration (known as AMS-01), the detector was installed on the shuttle Discovery during the STS-91 mission (2 - 12 June 1998). During the 10 days of this trial mission, AMS acquired data corresponding to approximately 100 millions of triggers, letting us understand how well it will behave during the ISS.
Following the precursor flight data analysis, a major upgrade of the detector has been proposed (called AMS-02), based on a superconducting magnet and on the addition of various detectors (Transition Radiation Detector - TRD, Ring Imaging Cherenkov detector RICH, Electromagnetic Calorimeter - ECAL). The upgrade allows AMS to extend the particle measurement and identification to very high energies (MDR = 1-2 TV).
AMS-01
The AMS-01 detector is based on a permanent Ne-Fe-B magnet with an analyzing power of 0.15 T m2 that contains 4 of the 6 layers of the Silicon tracker and the scintillator counters of the anticoincidence system. Each tracker plane measures the energy lost by the crossing particle and the position (x, y) with a resolution of 30 (x) and 10 (y) microns, from which the particle momentum and charge can be inferred.
The trigger is given by the time of flight (TOF) system, which measures the velocity of the traversing particles and their charge. Combined to the tracker measurements, this allows the determination of the particle mass and charge sign.
The detector is completed with a threshold Cherenkov counter, below the magnet, to improve the separation between electrons and protons up to 3.5 GeV.
| AMS-01 |
|---|
 |
I started my work on AMS during the R&D phase of the AMS-01 detector, simulating and testing different kinds of TOF counters in Bologna. During the production stage I analyzed their characteristics under cosmic rays and their behaviour under spatial condition (i.e. very low pressure, rapidly varying temperature and high ionization of the residual atmosphere, at 400km height). In particular, I analyzed the possible sources of electronic noise and power leakage in the MIR and ISS orbit environment.
Starting from October 1997, I participated in the AMS-01 integration phase, in Zurich (Switzerland), debugging the TOF hardware and DAQ chain. In the meanwhile, I wrote few components of the general AMS software, a large project designed in a Object Oriented fashion and written in C++, that is able to reconstruct the tracks from real particles traversing AMS or from MC simulated ones (the simulation being carried on by the program itself).
The AMS-01 detector was brought at NASA Kennedy Space Center (KSC), Florida, at the end of January 1998, for the integration with the shuttle Discovery. From KSC, I was able to send in Italy the first plot showing that the TOF resolution obtained from cosmic rays (CR) (about 120 ps) was indeed what had been proposed by the collaboration. Other details can be found in my thesis (http://www.bo.infn.it/ams/tesi/diegocasadei/, in Italian), the paper published on NIM A 437 (1999) 212-221 and the conference proceedings of year 2001 (see http://cern.ch/casadei/papers.html).
During the NASA STS-91 mission (2-12 June 1998) AMS-01 operated on board of the Discovery shuttle for more than 100 hours, taking about 100 millions of events. During this mission I was sitting in the Payload Operations Control Center (POCC), at NASA Johnson Space Center (JSC), Houston, Texas, looking at the behaviour of the TOF system through the on-line monitoring program I had developed at JSC during May 1998 (as documented by my internal note AMS Online Monitoring Tutorial, AMS Int. Note May 31, 1998).
I collected few pictures about AMS on STS-91... But the NASA site Shuttle-Mir Multimedia/Photo Gallery/STS-91 is the best resource!
AMS-02
Although the original design of AMS-02 was based on a superconducting magnet, generating a much more intense magnetic field than that of AMS-01, the permanent magnet was finally chosen because it guarantees a constant field for decades. The detector which has been installed on the International Space Station has 8 Si tracking planes to achieve better rigidity resolution. In addition, the RICH extends to higher energies the velocity measurement carried on with the TOF. Finally, the TRD and the ECAL improve the capability to distinguish between different particles.
| AMS-02 |
|---|
 |
Links
A good survey of the AMS features can be found in the description by Benjamin Monreal at MIT.
If you want the most recent data available, go to the AMS home page.