Beijing Time April 8, 2013, 23:00. The Alpha Magnetic Spectrometer (AMS) Collaboration, a large scale scientific project that Shandong University has been participating in, announced the publication of its first physics result in Physical Review Letters. This is the first physics result announced by the remarkable AMS project, which is led by Nobel Laureate in Physics Samuel Ting and has been in operation for over 18 years. The result shows that the AMS has identified in excess of 400,000 positrons (the antiparticle of electron), some of which may originate from pulsars, or the collision of dark matter particles that people have been searching for a long time.

Over the last few decades, both particle physicists and astrophysicists have been very interested in the positron fraction from primary cosmic rays. The underlying reason for this interest is that by measuring the ratio between positrons and electrons and by studying the behavior of any excess across the energy spectrum, a better understanding of the origin of dark matter and other physics phenomena can be obtained. In cosmology, dark matter is a type of matter that neither emits electromagnetic radiation nor interacts with electromagnetic waves. At present, scientists from different countries are trying to detect dark matters using different methods and look for the evidence of their existence using direct and indirect approaches. The identification of dark matters, if possible, will be a large step forward towards understanding the origin of the universe.

The first publication of the AMS Experiment is a major milestone for the AMS international collaboration. The results of the AMS show, at an unprecedented accuracy, evidence that dark matters may exist. The AMS, under the leadership of Nobel Laureate Samuel Ting, is one of the largest scientific programs worldwide at the end of the last century and beginning of this century.

The AMS is the first sophisticated particle detector to be installed in the space. Since its installation on May 19, 2011 until the present, it has measured over 30 billion cosmic rays at energies up to trillions of electron volts. Its permanent magnet and array of precision particle detectors collect and identify charged cosmic rays passing through AMS from the far reaches of space.

Over its long duration mission on the ISS, AMS will record signals from 16 billion cosmic rays every year and transmit them to Earth for analysis by the AMS Collaboration. Currently, the total number of positrons identified by AMS, more than 400,000, is the largest number of energetic antimatter particles directly measured and analyzed from space. The first result of AMS is based on only ~10% of the total data expected. The particles observed in the energy range 0.5 to 350 GeV are the subject of the precision study reported in this first paper. The fraction increases steadily between 10 GeV to ~250 GeV, and at energies above 250 GeV, the spectrum appears to flatten. These features show evidence that this spectrum may originate from the collision of dark matter particles or from pulsars in the galaxy. The normal operation of high-energy physical detector in outer space is a great success and it is an even greater achievement to successfully record and transmit a huge amount of data. The team from Shandong University under the leadership of Professor Cheng Lin spent seven years on the thermal system of the AMS, which solved a major engineering problem of the detection of particles in the space.

Shandong University started to participate in the AMS collaboration in March 2004. Professor Cheng Lin was the chief scientist of the thermal system of the AMS project, generally responsible for its research, design, manufacture and experiment. Under the leadership of Professor Cheng, over 30 scientists from Massachusetts Institute of Technology (MIT), Swiss Federal Institute of Technology Zurich (ETH) and the National Aeronautics and Space Administration (NASA) developed a newly designed ad hoc cooling pad, which has good ability of heat transfer and heat storage. With this cooling pad, the heat from power distribution and the operation of electronics and various detectors can be dissipated in real time; in the meantime, the pad can absorb heat when the Space Station faces the sun, and thus become a heat source to raise the temperature of the system. By ensuring efficient heat dissipation and the homogeneity and stability of the temperature field, this design solves a major problem for the operation of the AMS in the environment of the International Space Station.

The AMS has successfully gone through various extreme conditions in the past two-year operation in the International Space Station and made a marvelous contribution to the thermal control methods regarding operation of large scientific apparatus in the space. After the AMS was installed in the International Space Station, the research team of thermal scientists at Shandong University, under the leadership of Professor Cheng Lin, continued to control and monitor the operation of the thermal system and to record and examine the data. According to the practical situation of spacial operation, Professor Cheng revised the model of thermal control and developed several new models in order to overcome various extreme conditions. The temperatures of the AMS and all the detectors were maintained within the defined limits. Professor Samuel Ting highly commended Professor Cheng’s work.

Source: Institute of Thermal Science and Technology of Shandong University