IceCube: A Next Generation Neutrino-Telescope

In the year 2004 started the installation of IceCube, a high technology next generation neutrino telescope, at the South Pole, several thousands of meters below the surface of the Antarctic ice cap. With 5160 optical sensors distributed over a cubic kilometer of ice, IceCube will be the biggest particle detector world-wide. At first, the South Pole appears a strange site for deploying such an instrument. But there are crucial advantages that outweight the relative inaccessibility. The Polar ice being about 3 km deep and highly transparent is an ideal medium to detect the faint light signals emitted by charged particles produced by high-energy neutrinos. The necessary infrastructure on site is provided by the newly renovated Amundsen-Scott station.

The successful deployment and operation of the AMANDA neutrino telescope was decisive for the the grant of the IceCube project. AMANDA was successful in detecting high energy neutrinos, and the quality of the data allowed to reconstruct their direction and energy to a high accuracy. The detected neutrinos, however, were produced in earth's atmosphere, as products of collisions between cosmic rays and air molecules. No spectacular discoveries have been made so far, but AMANDA has substantially contributed to the present detection limits on candidates for dark matter, on the flux of magnetic monopoles and on the neutrino flux from various potential point sources inside and outside our galaxy. AMANDA has clearly demonstrated that the polar ice is a suitable medium for a large neutrino telescope and the analysis of AMANDA data has proven the science potential of such a detector.

IceCube will be about 30 times bigger and thus substantially more sensitive than AMANDA. The deployment of all 5160 optical sensors will be completed until 2011, but during the construction phase the deployed parts of the detector produce already high-quality data. The 677 optical modules of AMANDA were integrated into the IceCube array. In 2009 AMANDA was decommissioned. The schematic sketch shows the dimension of the three detectors. Just like AMANDA, IceCube will be deployed in vertical strings. Each IceCube string will comprise 60 optical modules (three times the number of modules attached to the much shorter AMANDA strings), as well as their power-supply and the cables for the signal readout. The modules at one string will be equally spaced at a distance of 17 m. Each string will be lowered into a vertical hole, drilled with pressurized hot water, such that the instrumented volume of the detector spans a depth range between 1450 and 2450 m. A total of 86 holes will be drilled, 80 of them will be regularly distributed over a surface of a square kilometer, the distance between two holes being 125 m. The other 6 holes are for the new dense Deep Core detector in the center of IceCube. Here the horizontal string spacing is 72 m and the vertical sensor spacing 7 m.

 
The optical sensors used in IceCube are so sensitive that they will respond even to a single photon. Still inside the optical modules, the photon signals are amplified, converted into electrical pulses and then translated into a digital signals. Therefore, each of the 5160 modules has its own mini-computer as well as a precision clock to measure the arrival time of the photons to an accuracy of 5 nanosecond (5*10^-9sec). From the depth, the digitized light signals are send over kilometer-long cables to the central data acquisition system in the South Pole station.

DESY in Zeuthen takes part in the IceCube project with the following contributions:

• Production and test of 1300 of the more than 5000 optical modules,
  
• development and manufacturing of electronic components for the data acquisition system,
  
• software development for the data analysis,
  
• development and test of new methods of particle detection.