IceCube’s Antarctic season ends with success

As darkness settles over the South Pole and the Antarctic winter begins, the IceCube Neutrino Observatory has something to celebrate: a great season on the ice.

The 2009-10 season wrapped up 10 days ahead of schedule, and increased efficiency with the hot-water drill translated to 25,000 gallons in fuel savings.

IceCube is an innovative physics experiment that uses a cubic kilometer of ice at the South Pole as a telescope, searching the universe for neutrinos.

“At the inception of IceCube, no one would have seriously considered the possibility that holes would be drilled to a depth of 2.5 kilometers in 24 hours, using only 4,000 gallons of fuel,” says IceCube principal investigator and University of Wisconsin–Madison physics professor Francis Halzen. “In fact, we originally proposed to do 20 strings per season, and the reviewers thought we were dreaming.”

Drilling ended on Jan. 20, with the season officially coming to a close Feb. 10. Twenty holes were completed this season, bringing the detector total to 79.

Since 2004, IceCube drillers and researchers have traveled to the pole to build the neutrino detector deep in the Antarctic ice. Neutrinos are miniscule particles without an electrical charge and almost without mass. These unique properties make it possible for them to pass through matter easily and make them difficult to detect.

The IceCube underground telescope, slated for completion in 2011, searches the edges of the universe for high-energy neutrinos coming from events such as gamma ray bursts and supernovas.

“The sheer scope and complexity of the IceCube project are a testament to the tremendous vision and drive of our researchers and their collaborators. We are looking forward to its successful completion. This is an exciting time to be pushing the boundaries of our scientific knowledge,” says Martin Cadwallader, dean of the UW–Madison Graduate School.

Construction of the detector requires drilling to a depth of nearly 1.5 miles. A hot-water drill bores holes in the ice and detectors are installed on cables and left to freeze in, creating an array of detector strings that record the time and intensity of neutrino events. Each string contains 60 detectors, known as DOMs (digital optical modules). At the surface location of each string are four DOMs frozen into bubble free ice tanks, comprising the “IceTop” array.

Original plans for IceCube, as approved by the National Science Foundation, called for 70 in-ice strings. The goal was 80 strings, if construction costs were favorable. Currently, the National Science Foundation supports 86 strings, six of them “deep core.” The deep-core strings are designed to record low-energy neutrino events and are financed by European funding agencies. All deep-core strings were installed this season, and the detector will be complete next season after the deployment of seven strings.

Project director Jim Yeck credits the success to “experience across the board,” saying, “The project’s success is possible through the unwavering commitment of the NSF and their funding partners in Europe and other countries. This support enables contributions by over 30 collaborating institutions. Once a season is under way, the focus is on the activities at the South Pole, but what happens on the ice is the product of months of preparation across the globe.”

NSF awarded UW–Madison the lead responsibility in building IceCube. The project itself is a collaboration between researchers from around the world, including Belgium, Germany, the Netherlands, Switzerland, Japan, United Kingdom, New Zealand and Sweden.