2008 IceCube Update - Section 4
IV. ICECUBE HARDWARE
IceCube was designed to be much simpler to deploy, operate and calibrate than its AMANDA predecessor. When it is complete in 2011, it will consist of 80 strings of photomultipliers, each containing 60 digital optical modules (DOMs). The strings are placed on a 125 m hexagonal grid. DOMs are placed on a string with 17 m spacing, between 1450 m and 2450 m below the surface. The surface electronics are in a counting house located in the center of the array.
Each string of 60 DOMs is supported by a cable that contains 30 twisted pairs (each pair is connected to two DOMs in parallel), plus a strength member and a protective covering.
In addition to the deeply buried DOMs, the IceCube Observatory includes a surface air shower array known as IceTop. IceTop will measure the cosmic-ray energy spectrum and composition, above a threshold energy of about 300 TeV. Combined measurements of electromagnetic showers (on the surface) and deep underground muons with IceCube provide a useful technique for measuring the nuclear composition of cosmic-rays. Combined events can also be used to check the pointing accuracy of IceCube. IceTop consists of 160 ice filled tanks, each 1.86 m in diameter. There are two tanks near the top of each string. Two DOMs are mounted in each tank to detect the Cherenkov photons from charged particles in the air shower.
The main task in IceCube construction is drilling holes for the strings of DOMs. This is done with a 5 MW hot-water drill, which generates a stream of 200 gallons/minute of 88°C water. This water is propelled through a 1.8 cm diameter nozzle at a pressure of 200 pounds/square inch, melting a hole through the ice. Drilling a 2500 m deep, 60 cm diameter hole takes about 40 hours. Deploying a string of DOMs takes about another 12 hours.
Because of the Antarctic weather, the high altitude and the remote location of the South Pole, logistics is a key issue for IceCube. The construction season lasts from roughly November through mid-February. Everything needed must be flown to the Pole on ski-equipped LC-130 transports planes.
IceCube construction began in 2004/5, when the first string was deployed. In 2005/6, eight additional strings were deployed, and, during 2006, data was taken with nine strings. In 2006/7, thirteen strings were deployed, followed by eighteen in 2007/8, leaving the detector half done.