1、翻译原文 Alpha Magnetic Spectrometer(AMS02)experiment on the International Space Station (ISS) Abstract The Alpha Magnetic Spectrometer experiment is realized in two phases. A precursor flight (STS-91) with a reduced experimental configuration (AMS01) has successfully flown on space shuttle Discovery in
2、 June 1998.The final version (AMS02) will be installed on the International Space Station (ISS) as an independent module in early 2006 for an operational period of three years. The main scientific objectives of AMS02 include the searches for the antimatter and dark matter in cosmic rays. In this wor
3、k we will discuss the experimental details as well as the improved physics capabilities of AMS02 on ISS. Keywords Alpha Magnetic Spectrometer, International Space Station, Antimatter, Dark matter Introduction A possible existence of cosmologically large domains of antimatter or astronomical anti obj
4、ects and the nature of dark matter in the universe are fundamental questions of the modern astroparticle physics and cosmology. The AMS02 experiment thanks to its large acceptance (0.65 m2) and its particle identification capability, will study these fundamental aspects with unprecedented sensitivit
5、y. This requires the measurement of the physical quantities such as particle momentum, charge and velocity with highest possible degree of confidence. An unambiguous proof of existence of cosmicantimatter would be observation of antinuclei (Z2)in cosmic rays. An observation even of a single antiheli
6、um or heavier nuclei would demonstrate that primordial antimatter indeed exists and it is not too far from us. The AMS02 will be able to distinguish a single antihelium nuclei among109 estimated background particles over 3 years. The project is realized in two phases. In June 1998, a baseline config
7、uration of the experiment has down on the space shuttle Discovery for 10 days mission on 51.70 orbit at altitudes between 320 and 390km. From this mission (STS-91) we gathered precious information on detector performance in actual space conditions and on possible background sources. AMS01 has also m
8、easured, for the first time, with such an accuracy from space, cosmic ray fluxes in GeV region covering almost the whole Earth surface.The detector layout, performance and the physics resuits of AMSO1 during STS-91 flight (AMS-0l ) are described in detail elsewhere. In this work we will discuss the
9、experimental configuration as well as the physics capabilities of AMS02 on the international Space Station. 2.Details of the AMS02 experiment The AMS02 is a large acceptance, high precision superconducting magnetic spectrometer designed to measure cosmic ray spectra of individual elements with Z106
10、were other key parameters for its design. The AMS02 will weigh 6760 kg and will have a power consumption of 2 kW. In the following the AMS02 sub-detectors will be described from up to downstream. 2.1 Transition Radiation Detector (TRD) The Transition Radiation Detector is designed to separate a/p si
11、gnals to distinguish e+ and p from relative backgrounds (p and e 一 respectively) with a rejection factor of 103 一 102 in the energy range from 10300 GeV. This rejection factor combined with the Electromagnetic Calorimeter will provide an over-all e+/p rejection factor of 106 at 90% of e+ efficiency.
12、 The detector consists of 20 layers of 6 mm diameter straw tubes alternating with 20 mm layers of 10 hum polyethylene/polypropylene fiber radiator. The tubes are filled with a 80% 20% mixture of XeCO2 at 1 bar from a recirculating gas system designed to operate in space for3 years. The wall material
13、 of straw tubes is a 72 m kapton foil. The upper and lower 4 layers run in the x direction (parallel to AMS02 magnetic field) while central layers run in the perpendicular y direction to provide bi-dimensional tracking and particle identification. 2.2 Time of Flight (ToF) system The ToF system is de
14、signed to provide fast (first level) trigger to the experiment, measurement of time of flight of the particles traversing the detector with up/down separation better than 10-g, the measurement of the absolute charge of the particle (in addition to dE/dX measured from the Silicon Tracker) and the ide
15、ntification of electrons and positron from antiprotons and protons up to 1-2 GeV. The expected overall time resolution is 140 ps for protons and better for heavier cosmic ray nuclei (see Fig.3 for intrinsic resolutions). It consists of four scintillator planes (see Fig.4) read by a total number of 1
16、44 Hamamatsu 85946 phototubes. The design of AMS02 ToF system is determined by the constraint of operation in 0.10.3 T stray magnetic field. The choice of PM and the shape of light guides are driven by this issue. Light guides are indeed tilted to reduce the angle between the magnetic field and PM a
17、xis. 2.3 Superconducting Magnet (SCM) One of the challenging features of the AMS02 detector is its strong superconducting magnet. It is the first large superconducting magnet used in space and it has a bending power of BLZ 0.8 Tm2 which will be essential to perform a sensitive search for antimatter(
18、He)in the rigidity (p/Z) range from 0.1 GV to several TV. The magnet consists of 2dipole coils together with 2 sets of smaller racetrack coils (see Fig.5) with a total cold mass of about 2300 kg. The racetrack coils is designed to increase the overall dipole field, to minimize the stray dipole field
19、 outside the magnet (max stray field at a radius of 3 m is 4 mT) in order to avoid an undesirable torque on the ISS caused by the interaction with the Earth magnetic field. All coils are wound from high purity aluminum-stabilized niobium-titanium conductor. The magnet will be operated at a temperature of 1.8 K and cooled by 2500 L of superfluid helium, which should be operational for three years without refilling (optimized for heat losses).
