IceCube scientists and engineers installed 480 new deep ice and 48 new surface Digital Optical Modules (DOMs) during the 2005-6 Austral season at the South Pole effectively doubling the size of AMANDA, the existing neutrino detector. Including the optical modules from previous seasons, over 600 IceCube optical modules and over 660 AMANDA sensors now comprise the current installation of the IceCube Neutrino Observatory. The IceCube team used a 5 Megawatt enhanced hot water drill to drill eight new 2.5 Kilometer-deep holes this season using two drill towers. The successful drilling program was due primarily to the strength and experience of the drilling crews and the various improvements made to the drill.
Commenting on this season the IceCube Principal Investigator, Francis Halzen said,
"The news is good all around. First, the digital optical modules deployed last year have now functioned for one year without failures. They perform like a Swiss watch. But the big story of the season is the performance of the drill. There is a famous quote about drilling: no good day of drilling goes unpunished. The IceCube drilling team has proven this wrong. Despite a delay of more than 10 days for improvements of the drill at the beginning of the season, we reached our goals for this year. All the major challenges encountered by drilling a first hole last season have been solved."
The use of a second drill tower this year enabled the drilling teams to set up and begin drilling the subsequent hole within 3 days of completing the previous hole, leapfrogging from location to location. As the season developed, the drill team drilled one hole every 5 days and in less than every 4 days at the end of the season. With an earlier start next year and a consistent cycle time of 4 days or less, more than 14 strings could be deployed each season, which starts in early November and lasts until February 15. Unpacking and setting up the drill equipment in November and disassembling and repacking in February reduce the time for drilling to about 60 days.
IceCube now has 9 digital strings and 16 surface detector stations in addition to the still running AMANDA array. Each of the deployed strings consists of 60 DOMs on a cable that is 2500 meters long and weighs 15 000 pounds. This season the deployment teams averaged 8 minutes per DOM for a typical deployment per string of 12 hours or less.
The newly installed DOMs are already sending up positive signals as they "freeze in," a process that will take several weeks. The deployment team at the South Pole inspected and certified 858 DOMs for installation this season and next. IceCube scientists will continue to verify the cable connections and surface electronics during the upcoming winter season.
Scientists, engineers, and technicians in the northern hemisphere in 2005 constructed over 20% of the total DOMs, cables, strings, and IceTop tanks required for the Neutrino Observatory.
In an email to the team at the South Pole after the eighth string was deployed Jim Yeck, IceCube Project Director, sent congratulations saying,
"I know that there is more work to be done but let there be no doubt about what a remarkable accomplishment it is to safely install eight strings this season ... IceCube construction is officially launched and IceCube operations and a productive scientific program is now possible."
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. When completed in about 2011, IceCube will occupy a cubic kilometer of deep Antarctic ice, from a depth of 1450 to 2450 meters. Nearly five thousand DOMs in the deep ice and in surface IceTop tanks will comprise the finished observatory.
Scientists from over 30 international institutions are beginning to evaluate the data coming from the DOMs installed so far. They will be looking for signals that indicate the neutrinos have survived the millions of miles of intergalactic travel, traveled through the northern hemisphere of the earth, and collided with the nucleus of an atom within a water (ice) molecule. These collisions result in muons that travel faster than the speed of light in ice and thus produce Cherenkov radiation. The DOMs see through the clear deep ice of Antarctica, detect the Cherenkov radiation, and send data to the surface data acquisition system (DAQ). Scientists analyze the data to reconstruct the path of the muon that travels in the same direction as the neutrino that created it.
Christian Spiering, spokesperson of the International IceCube collaboration expects that the "first physics results from IceCube will appear soon. At our April 2006 collaboration meeting in Baton Rouge we will discuss the performance of the installed equipment and ways to extract relevant physics data within several months."
The U.S. National Science Foundation funds the IceCube project, with significant contributions from Germany, Sweden, Belgium, Japan, New Zealand, the Netherlands and the Wisconsin Alumni Research Foundation. In the U.S., 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, the University of Wisconsin-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.