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Person gestures to long object on table.
Photo Credit: Peter Rejcek
Scientist James Roth discusses the drill head used in the hot-water drilling system for the ARA project. The new system pumps water out of the hole, leaving it dry, which prevents it from freezing back too quickly before the ARA instruments are deployed.

ARA refines hot-water drilling technology for installation of stations

Installation and design of the array is still ongoing. The first station was hot-water-drilled into the ice sheet in 2011-12, followed by two more in 2012-13. Like the IceCube Neutrino Observatory, the instruments for ARA are located within the ice sheet itself. However, where the IceCube instruments are up to 2.5 kilometers below the ice surface, ARA is only about 200 meters deep.

“It’s very different from IceCube,” Karle said.

Each ARA station consists of four holes of instruments spaced about 20 meters apart. Four antennae are lowered down on a cable, two horizontally polarized and two vertically polarized. Two additional holes contain instruments for calibrating each station, because also unlike IceCube, which detects thousands of other events, ARA is finely tuned for only ultra-high energy neutrinos.

Machinery sits in plywood box container.
Photo Credit: Peter Rejcek
The ARA system uses a hot-water drill that uses heaters similar to those employed at a car wash.

“There are no natural backgrounds anymore because you need a high-energy interaction in the ice in order to record those signals,” Karle explained “For ARA there is no background. You see nothing.”

Installation of a station is less labor intensive than IceCube, which employed dozens of drillers to build most of the under-ice telescope over the course of six summer seasons. The ARA team is still refining the drilling process, which involves using a hot-water drill to bore a hole through the ice.

The water is pumped out of the hole, leaving it dry so that it won’t refreeze – a problem encountered the first season because the holes are only about 15 centimeters wide.

“That’s what’s really unique to this year. It’s the first time drilling has ever been done that way: Hot-water drilling and pumping it out at the same time,” noted James Roth External Non-U.S. government site with the University of Delaware External Non-U.S. government site, which is part of both the IceCube and ARA collaborations.

Power for the drill comes from six heaters and a 50-kilowatt generator. Fuel tanks on site provide AN8 gas (a special blend that can withstand colder temperatures) to the heaters.

“It’s basically what you’d see in a car wash,” Roth said of the heaters used in the drill configuration, which includes a completely redesigned hose reel from what was used on IceCube. The drill control center was also redesigned at the University of Delaware. Drillers carry PDAs to monitor parameters like water temperature and flow.

“It’s been really helpful for the guys running the heaters,” Roth noted.

Last month, the project received additional funds to operate the test-bed stations to learn more about RF properties of the upper layers of the ice sheet, as well as develop additional hardware and software capabilities while the final design of the array is finalized.

Small building sits on a sled.
Photo Credit: Peter Rejcek
A small building on a sled is used to deploy the ARA string of antennae. The tiny structure in the distance is the South Pole Station.

ARA not only builds on the ground-breaking work done by the IceCube collaboration. Previous projects paved the way, including the Radio Ice Cerenkov Experiment (RICE), an experiment in the mid- to late 1990s that tested the potential of the radio-detection technique for measuring the cosmogenic neutrino flux.

In addition, the Antarctic Impulsive Transient Antenna (ANITA) External Non-U.S. government site experiment flew on high-pressure ballons at 35,000 meters in the 2000s to search for radio waves from extra-terrestrial neutrino interactions.

Many of the researchers involved in those experiments are part of the ARA program, according to Karle. Scientists from universities in Taiwan, Korea, Israel, the UK and Belgium are also working on the array.

“We have significant international contributions,” Karle said. “We have the potential to do particle physics that is beyond the reach of current experiments.”

NSF-funded research in this article: Albrecht Karle, University of Wisconsin-Madison, Award Nos. 1002485 and 1359526 External U.S. government site; Amy Connolly, The Ohio State University, Award No. 1359535 External U.S. government site; and Kara Hoffman, Peter Gorham and David Besson, University of Maryland College Park, Award No. 1002483 External U.S. government site.