A journey 
into Space via CERN

The AMS experiment is nearing the final phase of preparations for its journey to the International Space Station. The different parts of the detector are to be assembled at CERN.

The International Space Station on 19 June 2007. The AMS detector will be installed on one of the arms, as indicated by the arrow. Photo: NASA.

The AMS tracker in the clean room with its silicon sensors and electronic modules. Photo AMS collaboration.

The AMS superconducting magnet that will surround the tracker. Photo AMS collaboration.

Where has the antimatter of the early Universe gone? This is one of physics’ great unsolved mysteries. At CERN, the physicists have produced anti-atoms in large quantities and have long been using anti-particles in their accelerators. But there is virtually no antimatter in the Universe, and no source of it has been found.

The physicists’ goal is to find either an explanation for the disappearance of antimatter or else proof of its existence tucked away in a remote corner of the Universe. AMS (Anti Matter Spectrometer) will go where no antimatter experiment has ever gone before: the International Space Station (ISS). If a significant quantity of antimatter were to be detected on the ISS, it would constitute irrefutable proof that there is still an active source of antimatter in the Cosmos. The light antiparticles that are detected on the Earth or in the atmosphere are almost certainly the by-product of interactions. As well as hunting for primordial antimatter, AMS will look for dark matter by attempting to detect the annihilation products of the hypothetical supersymmetric particles. The experiment will also analyse the composition of galactic and extra-galactic cosmic rays.

In order to peer into the Universe with an unprecedented degree of precision, AMS is equipped with a tracker made up of about 6 square metres of silicon sensors corresponding to some 196,000 electronic channels. NASA’s strict quality requirements meant that only 2500 sensors of the some 4000 produced were able to be used. In order to comply with the conditions imposed by the journey into Space and the period of time that will be spent there, the glue used in the tracker’s construction had to be de-gassed. The tracker was completed this year and is being prepared for removal from the University of Geneva to CERN at the end of September. It will be surrounded by a powerful cryogenic magnet and other high-precision detectors. The whole detector weighs over seven tonnes.

AMS is the fruit of a collaboration involving Europe, the US, China and Taiwan. At CERN it has "recognised experiment" status. Various tests on different parts of the detector have been carried out at CERN using beams from the SPS. The final assembly and tests will be done at Prévessin, and CERN will be one of the data collection centres. AMS will remain on board the ISS for several years and will send out data throughout its time in Space.

"Constructing a particle detector that has to remain in Space for several years represents a huge technological challenge," says Martin Pohl, who is in charge of the project at the University of Geneva. "The physicists taking part in AMS mostly come from the world of accelerator particle physics. But equipment that has to be capable of withstanding 10 g of acceleration when the space shuttle is launched and cannot exceed 2 kW of energy demands ingenious solutions. This is the challenge the AMS represents".

The experiment must be ready at the Kennedy Space Centre, Cape Canaveral (Florida), by the end of 2008 at the latest.