Resume Reading — Ice Fishing for Neutrinos


Ice Fishing for Neutrinos

Ignorant and lucky at the bottom of the Earth.

One afternoon in February 2000, after a long day’s drilling, Bruce Koci and I sat together on the sand in the volcanic crater on…By Mark Bowen

One afternoon in February 2000, after a long day’s drilling, Bruce Koci and I sat together on the sand in the volcanic crater on the 19,000-foot summit of Kilimanjaro. As we leaned against our packs and watched the sun set, he reminisced about his career.

“I never was in the drilling business to be a driller. I hate machines. Maybe one of the few engineers in the world you’ll ever find that feels that way about them. I hate them … That’s one of the few times I will ever fly into a rage is over a machine that does something that it shouldn’t do.”

“I’m here for the experience. I came into this thing as a canoeist. I walked out of good aerospace job and decided to go into ecology and then got back into engineering through glaciology, starting at Minnesota. I’ve always come for the place; I haven’t come to do the drilling. I’ll do my damnedest to make sure the drilling goes well, because that means I can go to another good place.”

science on ice: The IceCube Laboratory at the Amundsen-Scott South Pole Station, in Antarctica. IceCube is a particle detector that searches for neutrinos from the most violent astrophysical sources, like exploding stars, gamma-ray bursts, and cataclysmic phenomena involving black holes and neutron stars. AMANDA was its predecessor.Erik Beiser, IceCube/NSF

He had not quite earned a degree in glaciology, and was, he recounts, “rapidly running out of time, when all of a sudden I got this call that the University of Nebraska was looking for someone with a degree in engineering and some understanding of glaciology. So I called them up, got hired over the phone in, like, mid-October, and was on a plane two weeks later for the Ross Ice Shelf.”

The Ross Ice Shelf floats on the surface of the sea by McMurdo Station in Antarctica and provides a stable platform for the station’s airstrip, Williams Field. It is the largest body of floating ice on the planet, about the size of France. Bruce first visited the place over the 1977–78 Antarctic summer.

The University of Nebraska had contracted with the National Science Foundation to drill a hole through the 200-foot ice shelf so that a group of scientists could study the ocean beneath. The drill was a so-called flame-jet, which is conventionally used by the mining industry to cut crystalline rock. It consisted of two 10,000-pound compressors, feeding air at a thousand psi to a modified jet engine—a huge Bunsen burner, basically—which was lowered into a roiling, water-filled hole, spitting out flame and partially combusted diesel fuel.

“Electrically, it worked fine. It was just, optically we weren’t sure what the hell we had done.”

“Well,” said Bruce, “it makes an awful racket … Lotta noise; lotta smoke; it’s real dirty … But it did drill through the ice shelf and relatively quickly. Provided a hole about 18 inches in diameter, so the scientists were then able to lower their things down and do their experiments.”

Over the next decade or so, he helped a glaciologist named Charley Bentley from the University of Wisconsin at Madison drill numerous short holes with a hot water drill— basically a glorified garden hose—in various parts of Antarctica, so that Bentley could drop charges of dynamite into the holes for seismic testing. He became adept at the sophisticated art of ice core drilling, in which a hollow, tubular drill with a smooth interior, threads on the outside, and sharp cutting teeth on the bottom is repeatedly lowered into the ice to carve out core segments and pull them up, one meter at a time. He drilled ice cores in Greenland and many locations in Antarctica, including the pole—and also found time to invent the field of high-altitude ice core drilling.

By the spring of 1990, Bruce was pretty much at the top of his game. He had participated in about 30 remote drilling expeditions altogether and was arguably the most accomplished practitioner of ice drilling in all its forms on the face of the planet. When the Polar Ice Coring Office’s director, John Kelley, walked into Bruce’s office and asked him if he’d be interested in helping a group of physicists drill some holes in Greenland in order to explore the possibility of constructing a neutrino telescope at the South Pole, he jumped at the chance. “Absolutely!” he remembered saying. “This is the neatest project I’ve ever heard of in my life! I’ll work at night if I have to and just not sleep.”

In August 1990, Bob Morse, a physicist at the University of Wisconsin, and Tim Miller, a grad student at the University of California, Berkeley, embarked for Greenland to conduct the first known ice fishing for muons—their fishing line consisting of three photomultiplier tubes that Morse had scavenged.

freeze frame: A sensor lowered into a hole in the ice.Jim Haugen, IceCube/NSF

Bruce prepared an ice core hole he had drilled the previous summer. Since ice core holes will collapse over time from shear forces in a glacier, he had reamed this one out to a depth of 217 meters. The physicists dropped their fishing line into the dry hole and took their first series of measurements. Then they decided they wanted to increase the optical coupling between the phototubes and the ice, so they asked the drillers if they had any liquid on hand that they could pour down the hole. Unfrozen liquid is scarce on the summit of Greenland, but there happened to be a tremendous amount of butyl acetate on hand, for use in keeping the GISP hole from collapsing. They poured enough of it into the hole to cover the string and took another round of data.

“I don’t know why we felt like we had to haul the string back up,” says Bob, “but we did haul the string up, and all of a sudden we saw this blue sludge all over everything … The butyl acetate had completely dissolved the outer jacket of the wires, and it turned all the snow and all the liquid in the vicinity this beautiful purple-blue color … We wondered if we had any light transmission at all, because everything seemed to be, heh … And we took pictures of the tubes going down, and then we took pictures of the tubes coming up, and the picture of the tube coming up made it look like a nice big grape snow cone. (Bruce called it a “blue slushy.”) There was blue in my gloves, blue in my clothes, blue in my face … It was the dye or whatever it was that’s normally in the cable … Electrically, it worked fine. It was just, optically we weren’t sure what the hell we had done.”

The fledgling AMANDA (Antarctic Muon And Neutrino Detector Array) collaboration, consisting of Doug Lowder, Tim Miller, Buford Price, Andrew Westphal, Steve Barwick, Francis Halzen, and Bob Morse, submitted a letter to Nature, which was published the following September. Francis believes this “letter launched the experiment” by showing that the idea of using polar ice for neutrino detection “was still crazy, but not that crazy.”

One reads that “the hole was filled with butyl acetate, an organic liquid chosen for its low freezing point and optical clarity.” There is no mention of blue slush. “We find these results very encouraging, and are planning more extensive experiments at the South Pole during the coming austral summer…”

This, warts and all, is how experimental physics is done. As Bob Morse writes,

Greenland is a really beautiful example of an experiment quickly thrown together to meet a window of opportunity—mistakes were made—and where flawed or less than perfect data is also very useful, as failure can be when in the right hands … This little pre-AMANDA experiment has all of the features of the later AMANDA and IceCube experiments. The later successes … were simply a matter of getting the bugs out of the deployments and data retrieval systems—not a trivial task … This is a rare example where the funding agencies had more faith in the data (flawed as it might be) than many of the experimenters …

Francis adds that “it’s pretty clear we had no idea what we were doing, and so this was real research, right?”

He suspected “that many people had had this idea, knew more about glaciology than I did, and obviously concluded it could never work.” “If we really had [known] what we were doing we would probably not have done it. And, in fact, it turns out that a lot of the things we should have known turned out not to be true.”

the ice drill: The five megawatt heating plant for the IceCube drill. Hoses carry hot water across the ice from the heating plant to where the current hole is being drilled. The large reel in the center holds the hose, which is nearly two miles long, used for drilling the hole.Ethan Dicks, IceCube/NSF

In lectures to young scientists today, he sometimes uses the early days of AMANDA as an example of the dictum, “Don’t read books. Do things. There’s nothing better than to be ignorant and lucky.” (It goes over well.) It is usually the young, unaware of accepted knowledge, who make original discoveries. He believes that the only reason he managed to do something original in his late 40s was that he was “like a young person again” in the sense of being naïve. “It’s only when you’re ignorant and you haven’t read all the books yet that you can do something original and new.”

He was now taking a clear step into experimentalism, which is not ruled by the pristine logic of theory. Not only do numerous practical and strategic considerations come into play, oftentimes the wisest course is to stop thinking for a while and just do it.

Not only had the drill gotten stuck, the flow in the hose had stopped as well. This is about the only situation you can’t get out of with a hot water drill.

Had he read what was then the definitive textbook on the optics of water and ice, for example, he would have “learned” that the absorption length of blue light in pure ice—the distance over which about two-thirds of the light will be absorbed—was about eight meters. That would have been a show-stopper. They would have given the phototubes back to Cline and Rubbia and gone home. If Cherenkov light really was absorbed in that short a distance, it would take something like 2 million phototubes to fill a cubic kilometer of ice, and the tubes alone would cost about $6 billion. Luckily, the book turned out to be very, very wrong. They obtained an estimate of 18 meters from the Greenland data, and even though it, too, turned out to be wrong, it was a step in the right direction.

A few years later, when they were still struggling to understand the ice but had seen signs that the absorption length was actually much longer than even 18 meters, the library in Madison mistakenly delivered the textbook to Francis’s office; it was meant for someone else. He started browsing through it, naturally, and when he came to the line about the eight-meter absorption length a chill ran up his spine.

In the austral spring of 1991, Bob Morse, Bruce Koci, Steve Barwick, and Tim Miller traveled south to do the first drilling for AMANDA. PICO, an experiment searching for direct evidence of dark matter, also tasked a drilling crew that included Bill Barber, a tall, good-natured, unflappable, and incredibly strong Brit.

The idea is to use a hose with a nozzle on the end to spray a parallel stream of hot water into the ice, and let the nozzle free-fall as it melts its way down. What you want in a hot water drill is a lot of very hot water at high pressure and a hose with a wide diameter and heavily insulated sidewalls, so that the water will stay hot as it goes down and carry as much heat as possible out through the nozzle and into the ice. (There’s a bit of a balancing act here, because you do want some heat to escape through the sidewalls in order to keep the water in the upper portions of the hole from re-freezing as the drilling proceeds.) Bruce once pointed out that in the same sense that a neutrino telescope can never be too big, “you can’t have too big a hot water drill either, ‘cuz the best hot water drill is the one that drills the hole instantly; it’s the most efficient.” This is a mental construct, obviously—a drill that will deliver an infinite amount of heat in zero time—but it gets the point across: You want a lot of heat and a huge hose.

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Bruce knew that Bucky-1 represented a serious compromise in both respects. The hose was only an inch in diameter, and the heating plant, which consisted of a gang of hot water boilers standing in the open out on the ice, produced only half a megawatt of power. The first hot water drill he had used on the Ross had produced two megawatts. “We knew [Bucky-1] was limited, but we didn’t know how limited, exactly, because it was the first time anybody really tried to go deep in ice this cold.” He calculated that by the time they got to 1,000 meters the heat that the water would lose on its way down would exceed the output of the heating plant. In other words, the bottom of the hose stood a good chance of freezing. He could play various games to try to keep it from freezing, such as raising and lowering the drill in order to reheat the water in the newly opened hole, but this would cost fuel, and it was a tricky business in any case.

“Hot water drilling is not for the faint of heart either,” he says. “We’re trying to keep water in some place that’s minus 50 degrees, and that’s not a good thing to do.”

The AMANDA team was keeper of a stellar attraction in the tubs that they used to heat water for their drill. Until NSF caught on and made them illegal, there were hot tub parties out at the drill site. It’s good they were having some fun, because the drilling was not going well.

On the second hole they got greedy and tried to go to 1,000 meters. This led to about the worst thing that can happen in hot water drilling.

“We stuck Bucky-1,” Bob later recalled. “He’s still there.”

“Yup, radar marker,” said Bruce.

Bob was asleep in his cubicle in one of the Jamesways in Summer Camp when a PICO driller named Dave Kestor poked his head through the curtain and whispered the bad news. (Since one of the three shifts is always trying to sleep, silence is observed in Summer Camp 24 hours a day.)

“What should we do?” Dave asked. “Are we going to put the instrument down or not?”

“God, I don’t know,” Bob replied, “but I think we probably ought to. We’ve invested this much in the hole. We ought to stuff whatever we can down there.”

He got out of bed and went to find Steve Barwick. “I said, ‘Steve, ah, they’ve stuck the drill.’ And Steve went ballistic at this point and went screaming—he didn’t know where Tim Miller was, so he went walking into every Jamesway at about three in the morning, screaming at the top of his lungs, ‘Tim Miller? Tim Miller? Where the hell are you? Where the hell are you?’ … And I thought that there was gonna be some construction worker, some 6-foot-4 guy, was gonna get up and just kill Steve. I thought Steve was going to die.”

“If we really had [known] what we were doing we would probably not have done it.”

PICO had detailed only two shifts to the drilling, each working 12 hours a day, and it was the night shift that had stuck the drill. Bruce was on the day shift, and although he didn’t sleep much during drilling operations—he’d hang around to keep his finger on the pulse even when he wasn’t on duty—he happened to be asleep when the disaster occurred. Not only had the drill gotten stuck, the flow in the hose had stopped as well. This is about the only situation you can’t get out of with a hot water drill.

“Everybody who’s ever done hot water drilling has made the mistake of going with not enough heat once in their life,” Bruce later observed. He thought they were lucky to have gotten as far as they had.

They tried to pull it out with Caterpillar D7 bulldozer.

According to Bob, “That goddamn hose was like a violin string … It necked down to about half its original diameter … Bill Barber was the only one that had the courage to go over there and stand while the hose was down the hole and take a hacksaw and cut through it. And we saw this hose, or heard this thing, disappearing at the speed of sound down this hole, like phewwwwww.”

And so, with the drill head and a significant portion of the hose down the hole, they acted on Bob’s first sleepy thought and deployed one of the Madison/Irvine strings anyway. For whatever reason—the hose in the way, the hole too narrow—it only went down 150 meters. Then they began worrying that light from the surface might wick down to the detectors and flood out any muon signals they might possibly detect. The photomultipliers were exquisitely sensitive; they were operating at what is known as the single photon level, which meant that they could detect individual particles of light.

“I just looked around and said, ‘We’ve got to plug that hole. What can we do to plug it?’ ” Bob recounts. “There was asbestos and some green garbage bags around—the eco people would shit a brick if they heard this: I started stuffing asbestos insulation into the bags to give them bulk and flicking them down this hole, trying to make a light seal … I think I threw down three or four. I threw down as many as I had.”

Experimental physics, blemishes and all.

Mark Bowen is a writer and physicist. He has written for Climbing, Natural History, Science, Technology Review, and AMC Outdoors, and has been involved in AMANDA and IceCube since 1998.

From The Telescope in the Ice by Mark Bowen. Copyright © 2017 by the author and reprinted by permission of St. Martin’s Press.

Lead image credit: Stephan Richter, IceCube/NSF

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