Alpha Magnet Spectrometer

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Alpha-Magnet-Spectrometer (AMS) describes two magnetic spectrometers ( particle detectors ) for the investigation of cosmic rays . AMS-01 was on a mission with the Space Shuttle in space , AMS-02 is in long-term use at the International Space Station .

AMS-01

AMS-01 before installation in the space shuttle

The prototype AMS-01 was successfully tested in 1998 during a ten-day flight with the space shuttle Discovery ( STS-91 ). The AMS-01 experiment was permanently installed in the cargo hold of the space shuttle on this flight.

Even during this short flight, the traces of over 100 million charged particles of cosmic radiation could be measured. References to more complex antimatter (i.e. atomic nuclei or atoms made up of several antiparticles) were not found, the previous experimental limits could be significantly improved. A total of around 3 million helium nuclei ( alpha radiation ) were detected. There was not a single anti-helium core under it.

AMS-02

AMS-02 at the ISS (top center)

The AMS-02 experiment is a modern particle detector that was supposed to measure the composition of cosmic radiation on the ISS from 2010 for a period of originally three years. Due to the decision to operate the ISS until 2020, the spectrometer was revised again at short notice in 2010. In this case, the cooled with liquid helium superconducting magnet spectrometer against a normal neodymium - permanent magnets exchanged to an operation of up to 18 years enable AMS-02. The superconducting magnet would only have survived about three years. Dispensing with the cooled magnet also means a loss of measurement precision, since the magnet has to guide the charged cosmic particles through five different detectors. However, this loss can be more than compensated for by more sensitive detectors and the longer measurement duration. Due to the crash of the Columbia space shuttle in 2003, the original launch date was postponed from 2003 to 2011. AMS-02 launched on May 16, 2011 on board the STS-134 mission to the International Space Station and was attached to its position on the remote side of truss element S3 on May 19, 2011 .

Scientific tasks

One of the tasks of AMS-02 is the search for antimatter, as expected in the context of some cosmological models as a relic from the Big Bang . The detection of a single anti-carbon nucleus would prove the existence of stars made of antimatter in the universe, since carbon could not be formed during the Big Bang. In addition, AMS-02 is able to measure the energy spectra from heavy nuclei to iron. These data will make it possible to better understand the propagation mechanisms of charged particles in the Milky Way and thus provide the key to search for the annihilation products of dark matter with great accuracy . In the context of supersymmetric models or Kaluza-Klein theories , anomalies in the energy spectra of positrons , antiprotons and photons are predicted that could possibly be detected with AMS-02.

Detector description

Schematic representation of the AMS-02
Mission logo

AMS-02 has a mass of 8.5 tons, the dimensions are 3.1 m × 3.4 m × 4.5 m and the geometric acceptance is 0.5 m² sr . A superconducting magnet with a maximum field strength of 0.86 Tesla, which would have been cooled to 1.8 Kelvin with superfluid helium, was originally planned for the central component of the detector . This was replaced by the 1,200 kg neodymium permanent magnet from AMS-01 with 0.15 Tesla to extend the running time of the AMS-02. Inside the magnet there is a double-sided structured silicon strip detector with an active area of ​​6.5 m². This measures the passage of charged particles on eight levels with a single point resolution of 10 µm. The trajectories of charged particles are curved in the magnetic field of this magnetic spectrometer . Based on the curvature, the momentum of the charged particles and the sign of the charge can be determined up to particle energies of 1000  GeV . The stability of the track detector is monitored with the help of a laser alignment system with a precision of 5 µm. The side of the track detector is surrounded by the anti-coincidence counter (ACC), which is supposed to detect the passage of charged particles to the side. With the help of a star sensor and a GPS receiver, the exact alignment of the experiment is monitored using fixed stars.

To determine the mass of the charged particles, the experiment is completed upwards by a transition radiation detector (TRD) and downwards by a ring image Cherenkov counter (RICH) and an electromagnetic calorimeter (ECAL). In order to measure the flight times and thus the speeds of the particles and to trigger the readout electronics of the other detector components, a time-of-flight mass spectrometer (ToF) with a time resolution of 150  ps is located above and below the silicon track detector . The heat output of approx. 2000 watts generated by the experiment is radiated into space with the help of radiators.

The experiment generates a data rate of approximately 7 GBit / s ( gigabits per second). By processing the data, the rate is reduced to 2 Mbit / s and then transmitted to the ground.

organization

AMS was built by an international collaboration that includes 500 physicists from 56 research institutes in 16 countries, in close collaboration with NASA . The project was initiated by Nobel Laureate Samuel Chao Chung Ting from the Massachusetts Institute of Technology , who still directs it today. In Germany, the I. Physics Institute of RWTH Aachen University and the Institute for Experimental Nuclear Physics of the Karlsruhe Institute of Technology are involved in the experiment. The research work in Germany is funded by the DLR .

Results

In April 2013, the AMS collaboration published the first results of the experiment. To this end, 30 billion particles were analyzed, including more than 400,000 positrons . The excess of high-energy positrons observed by the Fermi telescope and Pamela could be confirmed. The scientific benefits of AMS and the possible continued operation until 2024 are controversial.

See also

Web links

Commons : Alpha Magnet Spectrometer  - Collection of Images, Videos, and Audio Files

Individual evidence

  1. ↑ a b Nasa postpones the end of the shuttle program. Spiegel-Online, accessed May 7, 2010 .
  2. ^ STS-134 Mission Information. NASA, accessed May 16, 2011 .
  3. ↑ a b AMS-2: Facts
  4. ↑ FliegerRevue August 2011, pp. 38–41, In search of antimatter
  5. ^ First result from the AMS experiment. CERN, archived from the original on April 19, 2015 ; accessed on June 15, 2016 .
  6. ↑ Jan Hattenbach: AMS02 finds positrons, but no explanation , scilogs.de, April 3, 2013
  7. ↑ Jan Hattenbach: Particle detector in the cross fire , Spektrum.de, August 9, 2018