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 the 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 penetrative and interact only very rarely with matter. They are believed to be produced by different 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 the neutrino interacting with matter one needs very large detectors. The AMANDA detector is sensitive to the 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 like clear ice in order to efficiently propagate the light. The glacier at the South Pole is 2900 metres deep and extremely transparent at great depths. The detector, which is under construction, consists of optical modules deployed in hales in the glacier made using a hot water drilling 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 a cable up to the surface and read by the on-line computer. The drilling is carried out by the American Polar Ice Care Office (PICO) with the assistance of Swedish drillers from the Swedish Polar Research Secretariat.

The AMANDA-A detector which comprises 4 detector strings with 80 optical modules was deployed during the 1993/94 season at a depth of 800-1 000 metres. Due to air bubbles remaining in the ice it was necessary to go deeper. Ten detector strings with optical modules were deployed between 1 500 and 2 000 metres during both the 1995/96 season (four strings) and the 1996/97 one too (six strings). The quality of the ice at these depths was found to be sufficient for a neutrino detector. The deeper detector is named AMANDA-B10 and has been taking data since January 1997. During the 1997/98 season three additional strings were deployed at depths of between 1 200 and 2 350 metres in order to investigate the quality of the ice above and below the B10 detector. The ultimate goal is to build a detector with 80–100 detector strings and thereby reach a detector volume of about 1 km³. This project is called IceCube.

The AMANDA project is a joint collaboration between University of California, Berkeley, USA; University of California, Irvine, USA; University of Pennsylvania, USA; University of Kalmar, Sweden; University Of Stockholm, Sweden; University of Uppsala, Sweden; DESY-Zeuthen, Germany and University of Wisconsin, Madison, USA.

The work

People and scientific equipment are transported by air from Christchurch, New Zealand to the American base McMurdo and then to the Amundsen Scott station at the geographical South Pole. For the 1998/99 season (starting beginning of November and ending middle of February) the detector was serviced, the data acquisition system was upgraded with new trigger electronics and calibration of the timing and position of the detector elements was performed. Preparation and inspection of the drilling equipment was carried out in order to prepare for the 1999/2000 season when it is planned to deploy six new strings around the AMANDA-B10 detector. These new strings will complete the building of the AMANDA-2 detector. The detector was turned on again in the middle of February 1999.

Preliminary results

The AMANDA detector has been continuously taking data during the ”winter season,” from March to the end of October, since 1996. During the summer months, November–February, we have either been adding new strings or calibrating and upgrading the electronics for the detector. In the future we expect to be able to run continuously through the whole year without any interruption.

A first observation of neutrinos by the AMANDA detector has been published. About 110 neutrino candidates have now been selected from the data taken during 1997. One of these neutrino events can be seen in figure 1 which shows the ten strings in the AMANDA-B10 detector with a muon track passing upwards close to one string. The muon is produced by a neutrino interaction just below the detector. The neutrino itself has most probably been produced in a cosmic ray interaction in the atmosphere above the North Pole, has travelled through the entire Earth and has then interacted close to the AMANDA detector. The distance between the lower part of the detector and the upper part in figure 1 is 350 metres. The size of the circles in the figure is proportional to the amount of light observed by each light detector.

The AMANDA detector is now the leading detector in the world for high energy neutrinos. The analysis work is on-going and several interesting items are under study. The collaboration submitted 11 different contributions to the International Cosmic Ray Conference (ICRC) in August 1999.