During the 1990s, the AMANDA collaboration demonstrated the feasibility of using transparent ice at large depths in Antarctica for neutrino telescopes. The scientific goals set for these telescopes are to use neutrino particles from space to investigate the ‘‘dark matter” of the Universe and to search for the sources of the highest energy cosmic rays. Neutrino particles are extremely penetrative and interact very rarely with matter. It is anticipated that the neutrinos are produced by different violent processes in the Universe, and the ability to detect high-energy neutrino sources will open a new window through which to study the Cosmos. In order to compensate for the extremely low probability of neutrinos interacting with matter very large detectors have to be used. The neutrino telescopes are sensitive to the Cherenkov light emitted from electrically charged particles created by neutrino interactions deep in the ice. The transparent ice at the South Pole, where the ice sheet is 2 900 m deep and extremely transparent at large depths (Askebjer et al., 1997, Askebjer et al., 1998), is a very suitable detector medium for a neutrino telescope. The AMANDA neutrino telescope was constructed between 1995 and 2000, mainly at depths of between 1 500 m and 2 000 m, and the optical modules were deployed in holes drilled by pressurized hot water. The AMANDA detector has been successfully operative and is registering data since February 2000. As a result of the success of AMANDA the large IceCube Neutrino Observatory is now under construction at the same location.

The construction of IceCube began in January 2005. The complete observatory will consist of 4 800 optical modules deployed between depths of 1 450 m and 2 450 m in 80 strings monitoring a volume of about 1 km³. The digital optical modules for IceCube (DOMs) are considerably more advanced than those used in AMANDA, digitising the photomultiplier signals and transmitting all information in digital form to the surface. Timing calibration, which was performed manually and took several weeks for AMANDA, occurs automatically every two seconds for the whole IceCube array. On the surface above the neutrino telescope an air shower array, IceTop, will detect air showers from cosmic rays interacting in the atmosphere. The combination of IceTop and the detectors in the ice will allow calibration of IceCube using atmospheric muons as well as facilitate analysis of the chemical composition of the incoming cosmic rays. The AMANDA telescope is an integrated part of the IceCube observatory following the merger of the AMANDA collaboration with the new IceCube collaboration in 2005.

The ice work

Personnel and scientific equipment are transported by air from Christchurch, New Zealand to the American base McMurdo on Ross Island, and then to the Amundsen-Scott station at the geographical South Pole by Hercules aircraft. Heavy equipment can also be transported by sea once a year arriving at McMurdo in January–February.

The construction of the new IceCube Neutrino Observatory continued during the 2006/07 summer season. The drill for IceCube has a heating power of 5 MW compared with 2 MW for the AMANDA drill; it is more advanced and is designed to drill a 60 cm diameter hole in the ice down to 2 500 m in less than 40 hours. Despite the higher power and the larger depth of the holes the consumption of fuel per hole is less than for AMANDA. One IceCube string with 60 optical modules was successfully deployed in January 2005, and another eight strings were deployed during the 2005/06 season. In the season 2006/07 the hot water drill was slightly modified, based on experience gained during the previous season, in order to improve the performance. Thirteen new strings were deployed, giving a total of 22 IceCube strings in the ice of the 80 aimed for. In addition ten new IceTop stations were successfully deployed giving in total 26 running stations. The equipped ice volume of the 22 IceCube strings is already about five times larger than the volume of AMANDA. The telescope is modular and newly deployed strings are commissioned at the end of the season. The sensitivity of the observatory to detect neutrinos will thus continuously increase during the deployment period. The last string of IceCube is expected to be deployed in January 2011. For the next season, 2007/08, the aim is to deploy another 14–18 strings.

During the season of 2006/07 Sweden contributed with two technicians for the drilling operation and three scientists for testing and deployment of the modules. The Swedish scientists also participated in the installation of acoustic detectors into the ice as a test for a possible future extension of IceCube. While IceCube is not expected to be large enough for the highest energy neutrinos, by using an acoustic technique it may be possible to monitor a larger volume of ice than is possible with light detectors. A test array with three strings, each having seven transmitters and 7 × 3 sensors, were deployed at seven depths between 80 m and 400 m in three of the water filled IceCube holes immediately after the optical modules had been deployed.

Swedish Sven Lidström, who has been a driller for many years for AMANDA/IceCube, was one of three IceCube personnel to remain at the station over the winter season, arriving at the South Pole at the end of October 2006 and staying until November 2007. In total, 54 people stayed over the winter season 2007 experiencing temperatures down to -75°C.

Preliminary results

The 22 IceCube strings are performing very well and are registering data together with the AMANDA array. A report on the performance of the first string deployed (Achterberg et al. 2006a) as well as the first results on atmospheric neutrinos amassed from the data taken by the 9-string detector during 2006 (Achterberg et al., 2007a) have already been published showing that the new IceCube technology works very well.

The analysis of data taken by the AMANDA telescope is still in progress. A general paper on principles and first results was published in Nature (Andrés et al., 2001). More than 4 000 neutrino candidates have been recorded, but so far, no evidence for extraterrestrial neutrinos has been found. About 30 scientific papers in refereed journals have been published. These include papers on:

• the search for neutrino point sources during the five years AMANDA has been running (Achterberg et al., 2007b)
• the search for neutrinos from dark matter annihilations in the Sun and in the Earth (Ackermann et al. 2006b, Ackermann et al., 2006c)
• the ice properties in the AMANDA volume (Ackermann et al., 2006d)
• the search for neutrinos from Gamma Ray Bursts (GRB), which are the most powerful explosions in the universe (Achterberg et al. 2006e, Achterberg et al., 2007c).

The acoustic test system has been functional and data has been recorded continuously. Analysis of the data is ongoing but while the noise level appears to be favourable there still remain questions regarding the characterisation of the noise and the acoustic properties of the ice.