AMANDA at the South Pole

ERNIE MASTROIANNI Journal Sentinel staff
Originally published Jan. 15, 2001

Amundsen-Scott South Pole Station -- About a year ago, University of Wisconsin graduate student Katherine Rawlins was working 12-hour shifts at the South Pole.
Outside.

Jet heaters kept the 30-below chill at bay while she double-checked the electronics of basketball-sized spheres that would soon be lowered into holes 2 kilometers deep.

She was part of the team building AMANDA, the $10 million neutrino detector made by an international consortium led by the University of Wisconsin-Madison.

This year, AMANDA is complete, Rawlins gets to work inside, and an increasing number of researchers and scientists from all over the world have joined her.

Their goal? UW-Madison physicist Robert Morse, the principal investigator for the project, puts it simply: "We're trying to understand the evolution of the universe."

The crystal-clear ice below the South Pole is an ideal place to place AMANDA, which looks for traces of violence on an unimaginable scale from the far reaches of the universe.

"Neutrinos," says UW-Madison physicist Francis Halzen, "are produced only by very violent processes."

Inside AMANDA


If you could see through the ice, AMANDA would be a cylinder, 200 meters wide and nearly 2 1/2 kilometers deep, made of hundreds of light-sensitive spheres. AMANDA is based on a theory by Halzen, who believed the idea would work even before the first schematics were drawn.

When galaxies collide, it's thought that the black holes in their centers are merging, according to Halzen. A black hole is matter so dense, that nothing, not even light, can escape its gravitational pull. A cubic centimeter might weigh as much as the Earth.

So, envision two of these heavy objects colliding, and you get an idea of the amount of energy that could be released. Neutrinos are thought to be products of such a collision.

AMANDA also has the potential to discover mysterious dark matter particles, which are thought to make up most of the matter in the universe. It can search for the birth of supernova explosions and the birth of super-massive black holes in the center of distant galaxies, according to Morse's proposal to the National Science Foundation, which pays for this unique research project.

Neutrinos are nearly massless atomic particles that carry a lot of energy in small packages.

But there's a problem detecting them. They have no charge. They don't react with anything and are nearly impossible to track. But they head out in a straight line from whatever violent reaction produced them. Billions of them pass through the Earth every day. But every once in a while, a neutrino will hit a molecule's nucleus. If that molecule is in ice or water, the collision will create a dim blue wake of light called a muon.

This is what AMANDA sees, and the hope is that with a proposed detector 10 times larger, called ICE CUBE, scientists will be able to pinpoint a distant neutrino source, which will help solve some conundrums that face today's astrophysicists.

"We don't really know what we are going to see," Halzen admits. He draws an analogy with photography.

"Suppose you have a camera, and it is capable only of black-and-white pictures. If black-and-white images were all you knew, trying to make a camera that would take color pictures would be hard.

"But we have to think of certain possibilities before we build."

Practical matters

While the theorist Halzen postulates what might be, it is up to UW-Madison's Morse to stage-manage the brain power and hardware at the South Pole where the massive project must first be calibrated, then put into operation.

Some have called it an ice telescope, but a clearer analogy might be to call it a giant antenna, with dozens of the world's most creative astrophysicists working hard to tune it in, to reveal the clearest picture possible.

The AMANDA project has already taken over an entire wing at the South Pole station's Martin A. Pomerantz Observatory. Incoming data is sifted through powerful computers, running programs that sift out the noise from the signals. Morse travels to the South Pole every year, to oversee the exotic work that goes into calibrating this one-of-a-kind detector.

This is a big year for AMANDA. All the holes are drilled, the photo multiplier tubes are in place, and Morse has been coaxing the detector to life, fixing broken things and calibrating the instrument.

Rawlins explains that the summer includes three stages of work.

"Beginning this summer, there is a huge calibration effort. In the middle of the summer, we fix problems. At the end of summer, we'll prepare the detector for a winter of running."

Rawlins is here for the middle part. "I'm going to be spending a lot of time looking at signals coming out of the ice," she says.

Rawlins' boss is UW-Madison physicist Albrecht Karle, who is directing the multinational AMANDA effort this month.

Karle has published one of the first scientific papers on AMANDA, which establishes the sensitivity of AMANDA as a detector for the more common atmospheric neutrinos, which originate from the sun.

On a recent Friday night, he was meeting in a galley at the Amundsen-Scott South Pole Station with Rawlins and Jim Madsen, a UW-River Falls physicist who is participating in AMANDA as part of a National Science Foundation outreach program. With them were three other researchers from Germany. They were discussing if it was better to use AMANDA as it has been set up or to make some difficult adjustments that would likely improve its performance.

Said Rawlins, "Some people want to work under the hood, and some people want to drive the car."

Bigger things

Soon, though, they may have a much bigger vehicle to drive.

Halzen says that AMANDA is a 10% prototype for the much larger ICE CUBE, a plan to put nearly 5,000 sensors in a cubic kilometer of ice beneath the South Pole. And it may take ICE CUBE to accomplish what Halzen and Morse want to do.

But ICE CUBE will not come cheap. Its cost has been estimated at nearly $250 million -- an amount that will need to be approved for the budget by President-elect George W. Bush. If it passes muster, it will be, by far, the largest project ever seen here.

Prospects for approval seem good, according to some in the science community.

Robert Gehrz, an astrophysicist at the University of Minnesota and past chairman of the American Astronomical Society, calls the AMANDA experiment -- with which he has no association -- "a technical marvel."

"It has a chance to get funding," he says, "because the physics community is behind it."

But, Gehrz adds, "It is so expensive, it can only be done by national will."

TRACKING LIGHT

THE TELESCOPE THAT LOOKS DOWN

Most telescopes look up. AMANDA, (Antarctic Muon and Neutrino Detector Array) looks down. It seeks to capture light from high-energy neutrinos coming up through the Earth. This telescope goes to extremes: It is buried in more that a mile of ice at the South Pole, where it seeks muons that emit a dim blue light when passing through AMANDA. Using this device, the light can be tracked back to a source in deep space.

200M

Snow layer

Heating plant

Depth 50 METERS

-- AMANDA detects high-energy neutrinos from distant sources deep in the universe. Twenty-three strings of widely spaced photoamplifier tubes are placed into deep, water-drilled holes in the South polar ice cap.

-- To drill the holes, water is heated to 190 degrees and pumped at a rate of up to 200 gallons per minute through a sophisticated nozzle that melts the polar ice and bores straight down.

-- About 10 tons of equipment goes into each of 23 holes.

-- More than 2,400 feet of crystal-clear ice rests below. Earth acts as a filter to block out any other cosmic noise from the north.

PHOTOAMPLIFIER TUBE

-- Photoamplifier tubes encased in clear glass spheres, larger than a bowling ball.

-- Tubes can detect the light from just one photon and amplify the signal one billion times.

-- Each photo detector sees the muon at a different time and brightness.

High-energy neutrinos coming up through the Earth will occasionally interact with ice or rock and create a muon; such a muon emits a dim blue light when passing through AMANDA, where it is detected and tracked back to a source in deep space.

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