The AMANDA detector for high energy cosmic neutrinos is under construction deep in the glacier at the Amundsen Scott Base at the South Pole, Antarctica. The scientific goals are, among others, to use neutrino particles to investigate the question of the dark matter of the universe and to search for the sources of the highest-energy cosmic rays. The neutrino particles are extremely penetrating and interact only very rarely with matter. They are thought to be produced by various processes in the universe, and the possibility of detecting high-energy neutrino sources will open a new window in the study of the cosmos. In order to compensate for the extremely low probability of neutrinos interacting with matter, one needs very large detectors. The AMANDA detector is sensitive to Cherenkov light emitted from muons created by neutrino interactions deep in the ice. In detectors of this type it is necessary to have a very transparent material, such as clear ice, in order to propagate the light efficiently. The glacier at the South Pole is 2900 metres deep and extremely transparent. The detector, which is under construction, consists of optical modules deployed within holes in the glacier drilled by a hot-water technique. The optical modules are photomultipliers contained in pressure vessels made of spherical glass. The photomultipliers are sensitive to single photons in the wavelength range from 330 nanometers (nm) to 600 nm, and have a diameter of 20 cm. The signal from each photomultiplier is transmitted via cable to the surface and read by on-line computers. The hot-water drilling is performed by the American Polar Ice Core Office (PICO), with the help of Swedish drillers from the Swedish Polar Research Secretariat.

The AMANDA-A detector, consisting of four detector strings with a total of 80 optical modules, was deployed during the 1993/94 season at a depth of 800-1000 metres, but due to air bubbles in the ice it was deemed necessary to go deeper. Ten detector strings with optical modules were deployed between 1500 and 2200 metres depth during the 1995/96 (four strings) and 1996/97 (six strings) seasons. The quality of the ice at these depths was found to be sufficient for neutrino detector operation. The deeper detector is named AMANDA-B10 and has been recording data since January 1997. During the 1997/98 season, three additional strings were deployed at depths between 1200 and 2350 metres in order to investigate the quality of the ice above and below the B-10 detector. The final goal is to build a detector with 80 detector strings reaching a detector volume of about 1 km3. This project is called ICECUBE.

The AMANDA project represents collaboration between: Brussels Free University, Belgium; University of California, Berkeley, USA; Lawrence Berkeley National Laboratory, Berkeley, USA; University of California, Irvine, USA; University of Pennsylvania, USA; University of Kalmar, Sweden; University of Mainz, Germany; University Of Stockholm, Sweden; University of Uppsala, Sweden; DESY-Zeuthen, Germany; University of Wisconsin, Madison, USA and University of Wuppertal, Germany.

The work

People and scientific equipment are transportedby air from Christchurch, New Zealand to the  American base, McMurdo, and then on to the Amundsen Scott Station at the geographical South Pole. For the 1999/2000 season (starting at the beginning of November and ending in mid-February) six new strings were deployed at a radius of 100 metres around the centre of the detector. This was part of the ongoing deployment of the outer ring of AMANDA (the three strings deployed in 1997/98 were the first of this extension). One of the strings (number 17), however, became stuck at 1500 metres depth instead of reaching 2000 metres. The reason was that the diameter of the hole was too narrow at this depth. A new procedure for checking the holes produced by the drilling team will be introduced to avoid this problem in the future. AMANDA has successfully deployed a total of 22 strings while only losing one. The lost string will degrade the detector, but not significantly enough to reduce the sensitivity. These six (five, taking in to account the lost string) new strings mark the completion of the AMANDA-2 detector. Three Swedes, Lotta Järnmark, Anders Pettersson and Jonas Kalin, took part in drilling the holes.

The Swedish physicists at the South Pole took part in preparing and deploying the new strings and in testing and improving the detector electronics. The data acquisition system was upgraded with completely new trigger electronics (a new trigger was designed and built by the Uppsala group). Calibration of the timing and position of the detector elements was performed (mainly on the AMANDA-B13). The six new strings could only be partially calibrated before the summer team left the Pole in mid-February 2000. This calibration will be done in the 2000/01 season.

The entire detector was turned on again in the middle of February 2000.

Preliminary results

The AMANDA detector has been recording data continuously during the winter season – March to the end of October-since 1996. During the summer months of November-February we have either been adding new strings or calibrating and upgrading the electronics of the detector. In the future we expect to be able to run the detector continuously throughout the year with few interruptions.

The results of preliminary observation of neutrinos by the AMANDA detector have been published. About 200 neutrino candidates have now been selected from the data recorded during 1997. These are compatible with the expected rate of neutrinos coming from cosmic ray interactions in the atmosphere. Several analyses using the 1997 data are now almost finished, and will soon be submitted for publication. The collaboration submitted 11 different contributions to the ICRC conference in August 1999.

The AMANDA detector is now the world’s leading detector of high-energy neutrinos. Prompted by the success of AMANDA, the collaboration has submitted a proposal for a new larger neutrino telescope, IceCube, to be built close to the AMANDA site. This will be decided on in 2001, and if approved, the first strings will be deployed in 2002/03.