Brief Introduction

　　The Alpha Magnetic Spectrometer (AMS) experiment is a large international collaborative program under the leadership of Professor S. C. C. Ting, a famous physicist and a Nobel Prize laureate in physics. 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 “Discoverer” 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 2005, 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)

　　6. Synchrotron radiation detector (for determining the charge sign of particle with high momentum)

The above-mentioned upgrades constitute the second stage project of AMS, known as AMS-02.

Research Topics

　　1. AMS – 01 (the first stage project of AMS, accomplished)

　　The crux in realizing the above-mentioned physics goals is for the large magnet operating in space to tell the signs of charged particles, precisely measure their momenta and identify particle types by working together with other measuring instruments. Chinese scientists have made important contributions to the AMS program. During Professor S. C. C. Ting’s China visit in 1994, he was given a start of joy when he learned that the Institute of Electrical Engineering (IEE), CAS had made important progress both in the theory of permanent magnet and its application research. Scientists of IEE proposed that the permanent magnet be made of Nd-Fe-B. Permanent magnet made of this kind of material has a strong magnetic field, a low magnetic leakage and a small magnetic bipolar moment. Being a permanent magnet, it does not need power supply and is convenient to accommodate in the outer space magnetic spectrometer.

　　An ideal solution to the difficult question that has puzzled the space magnetic spectrometer for years is finally found. Soon afterwards, Professor S. C. C. Ting made a proposal to the Department of Energy on AMS research in terms of sending in outer space the magnetic spectrometer made of Nd-Fe-B for the detection of antimatter and dark matter. He wrote in the proposal, “The latest development of the Chinese technologies for making permanent magnets has made AMS experiment possible.”

　　Taking part in this international collaboration are IEE, IHEP, the Center for Space Science and Applied Research (CSSAR), the Chinese Academy of Launch Vehicle Technology (CALVT) with IHEP as the coordinator. The Ministry of Science and Technology, CAS, the National Natural Science Foundation of China, the China Aerospace Industrial Corporation and the former Ministry of Metallurgy have given great support to this program. The Institute of Physics and Chung Shan Institute of Science and Technology from the Taiwan region have also taken part in this collaboration. IEE, CALVT and IHEP succeeded in developing a large permanent magnetic system for AMS in March 1997.

　　The AMS permanent magnet is 1.2m in diameter and 0.8m high, and weighs 2 tons. It is composed of 4000 pieces of Nd-Fe-B, connected with epoxy piece by piece. The intensity of the central magnetic field is up to 1400 gauss. Upon completion, the China made permanent magnet was airlifted to Switzerland to be assembled with other detectors. Following the integral test, AMS was airlifted to the Kennedy Space Launch Center. The magnetic design is very delicate with the magnet divided into 64 bars in the F direction and the magnetic direction continuously changing, thus ensuring the concentration of the magnetic field in the magnet. That is to say, there is a strong magnetic field only in the space surrounded by the permanent magnet and that the magnetic field drops below 1% at the place 50cm away from the magnet. And at the same time, the magnetic bipolar moment is very small. The specifications of these performances are critical to space experiments.

　　If the magnetic spectrometer has a large magnetic leakage, which means there is a strong magnetic field outside the whole facility, it will pose a serious threat either to the airlift or to the safe flight of the space shuttle and space station. Therefore, airlines of all countries and NASA have formulated strict safety regulations. The large permanent magnetic system developed in China fully agrees with the requirements of AMS experiment and the strict safety standard of NASA, thus withstanding the test of the first flight.

　　IHEP has designed and developed the veto counter for AMS with the counting rate reaching over 99.999% and the size allowances completely meeting the strict design requirements.

Considering the specific conditions of space launch and experiment in outer space, all the China made components had been subjected to severe tests in simulated space environment, including 20 odd oscillation tests done at the Beijing Satellite Environmental Engineering Institute and the 17.7g centrifugal test at the Chinese Hydraulic Science Institute. It turned out that all these components had met the design parameters. It can be said that the work done by Chinese scientists for the AMS international collaboration is first-rate and blameless. According to practice, NASA has to subject the instruments and facilities to reviews on safety thrice before they are sent into space. But the third review was cancelled because of the satisfactory and convincing answers of Chinese scientists to all the questions raised by the review committee. The answers were based on strong theoretical support and meticulous, careful, solid and reliable data. The cancellation of the stipulated number of reviews by NASA is unprecedented in its history.

　　To acknowledge the Chinese side for its excellent work, the AMS Collaboration Group gave a special permit for the Chinese souvenirs to be carried during this flight. These souvenirs include a gold plated memorial tablet and a copper memorial tablet with the inscription by Comrade Deng Xiaoping and the pattern by drawing master Wu Zuoren for the Beijing Electron Positron Collider, and also a copper tablet engraved with the name of the Institute of High Energy Physics, the Chinese Academy of Sciences.

　　2. AMS – 02 (the second stage project of AMS, in progress)

　　The electromagnetic calorimeter known as AMS - 02 developed by IHEP scientists in collaboration with their colleagues from CALVT, Italy and France is a critical subsystem in search for dark matter and for research on g physics.

　　The research contents and goals of this project include:

　　1) Development of AMS – 02 electromagnetic calorimeter　 

　　The AMS – 02 electromagnetic calorimeter is composed of lead and scintillating optic fiber glued together with the size of 658mm ´ 658mm ´ 250mm. Signals from 1296 readout channels of 324 photomultipliers are used for the precise 3-D measurement of the shower. The electromagnetic calorimeter has the following capabilities:

　　To measure electron and photon up to 1 TeV;

　　To reshape the electromagnetic shower with high accuracy;

　　The identification ability of electromagnetic and hadronic shower can reach 10-4. It can lower the background of proton (antiproton) which is 104 larger than that of positron (electron) and increase the detection efficiency of electron to 90%;

　　To work under the condition of magnetic field and

　　To withstand the temperature variation of -400C—+400C in space.

　　2) Mechanical design of the electromagnetic calorimeter structure and construction　

The mechanical structure includes the upper and lower honeycomb, 4 side plates and the connecting parts of the space shuttle. ECAL is the most important sub-detector of AMS that weighs 595kg. But the supporting structure weighs only 67kg.

　　The carrying coefficient of ECAL demanded by NASA is the strictest compared with that of all other sub-detectors of AMS. The combination load: Nx=±7.8g, Ny=±7.8g, Nz=±11.1g; the rotation load: Rx=±148rad/sec2, Ry=±123rad/sec2, Rz=±51rad/sec2.

　　The structural thickness of the upper and low plate is 25mm each and the required carrying capacity is 11.1g × 1.4 to support a weight of 600kg. The main structure of ECAL is made of glued components. Safety must be ensured when the glue no longer has any effect.

　　There are 90 or 72 holes in the side plates for installing photomultipliers, whose frames are narrow. Its support structure should withstand the large loading of the shuttle during its take-off and landing.

As it is directly installed in the American USS-II support, it should bear a large accelerating loading.

3) Space environmental tests of the electromagnetic calorimeter

　　The model, prototype and flight model are fabricated for the main body of the detector ad then subjected respectively to the tests of simulated space environment, including oscillation test, centrifugal test, thermo vacuum test, etc.

　　Measurements of physics performances both before and after the detectors and readout electronics are subjected to tests of simulated space environment to ensure that the detector system can meet the requirement of the space environmental tests

　　4) Development of the trigger system of the electromagnetic calorimeter

　　The electromagnetic calorimeter serving as SRD to trigger TeV electrons. As the SR readout time is slow, ECAL is required to have a very high rejection ratio for high-energy protons and the trigger rate lower than 2 Hz.

　　Using ECAL signal to veto the veto counter in order to prevent the event reverse scattering from lowering the trigger efficiency of electron events of veto counter,

　　M-C simulation and optimization of the two trigger methods of Logic and Analog, determination of the trigger method, completion of the design of electronics circuits and fabrication of electronics.

　　5) Study and measurement of the performance of the electromagnetic calorimeter

　　Test of the 324 photomultipliers, calibration of their performance and building of the performance database.

　　Beam test of the electromagnetic calorimeter at CERN to measure and study the stability of detectors, the energy resolution and linearity, and the performance of the readout electronics system of the photomultipliers.

　　6) Monte Carlo simulation program and reconstruction system

　　Development of Monte Carlo program for detector simulation computation. Optimization of the detector structural design and readout mode by taking into account energy resolution, e/p,e/p separation and position resolution.

　　Development of an event reconstruction program system for AMS-02 to supply the developmental information of shower bunch, and energy deposition, and to identify impacting particles.