IceCube telescope construction exceeds season goals

As the austral summer wanes, so does the highly successful 2006-07 work season at the IceCube Neutrino Observatory in Antarctica, which draws to a close Thursday, Feb. 15.

During a productive season, scientists and engineers successfully positioned 13 strings of optical sensors deep in the polar ice. Each string carries 60 of the digital optical modules (DOMs), which are designed to capture evidence of highly energetic and elusive subatomic particles called cosmic neutrinos. This year’s efforts more than doubled the number of installed DOMs to a total of 1,320, roughly one-fourth of the 4,800 sensors that will ultimately make up the IceCube Neutrino Observatory when it is completed in 2011.

Neutrinos released by distant, high-energy cosmic events travel through space largely unaffected by matter or gravity. By seeking to identify the sources and distribution of the highest energy neutrinos, IceCube will provide a new window to the universe to answer questions about supernovas, dark matter, gamma-ray bursts and other exotic cosmological mysteries.

To construct the observatory, the IceCube team uses a specially designed five-megawatt hot-water drill to bore more than one and a half miles down into the ice, then lowers the sensors on cables and allows the ice to refreeze around them. When completed, the observatory will span a cubic kilometer of deep Antarctic ice along with a series of surface IceTop tanks.

Despite the challenges presented by extreme working conditions at the pole, the scientists surpassed progress expectations this year and are optimistic for upcoming seasons.

“This season at the South Pole was a fantastic success,” says project director and University of Wisconsin–Madison researcher Jim Yeck. “The construction project is on extremely solid footing with the general expectation that we will exceed our baseline installation goals in future years.”

Another major accomplishment of the season was the construction of the new IceCube Lab, which houses the powerful computers that collect, sort and store the massive quantities of data recorded by the DOMs. A small percentage of the data will be transmitted via satellite, while the rest will be shipped to Madison on magnetic tapes.

Scientists from more than 30 international institutions are already beginning to evaluate the data coming from the DOMs installed so far. “With one-fourth of the detectors already in place, we can do science now. We don’t have to wait until 2011,” says UW–Madison’s Francis Halzen, principal investigator of the IceCube project.

High-energy neutrinos can act as intergalactic messengers, says Halzen, carrying information about distant cosmic events like exploding stars. Though neutrinos cannot be seen directly, the scientists are using the IceCube telescope to capture evidence of collisions between these cosmic neutrinos and the atoms of water that make up the Antarctic ice. Each collision releases a tiny flash of blue light that can be detected by the DOMs. Scientists analyze the data to reconstruct the path of the neutrino and, hopefully, its origin.

“Whatever nature will tell us, we are now ready to hear,” Halzen says.

The IceCube project is funded by the National Science Foundation, with significant contributions from the Wisconsin Alumni Research Foundation, Germany, Sweden, Belgium, Japan, New Zealand and the Netherlands. In the United States, the project involves scientists from UW–Madison, the University of California at Berkeley, the University of California at Irvine, the Lawrence Berkeley National Laboratory, the University of Maryland, Penn State University, UW-River Falls, the University of Delaware, the University of Kansas, Clark Atlanta University, Southern University, the University of Alaska and the Institute for Advanced Study.