Neutrino fishing

Ignorant lucky at the very bottom of the Earth

One afternoon in February 2000, after a long drilling, Bruce Kochi and I sat on the sand in the crater of the volcano on the top of Kilimanjaro at an altitude of 5600 m. We sat leaning against our backpacks and watched the sunset, while Kochi remembered our career.

“I’m not in this business to be a driller. I hate cars. I may be one of the few engineers in the world who treat them that way. I hate them. The rare cases of rage that happened to me came from the machines that are not doing what they should do. ”

“I do this because of the experience. I did paddling, then I left a good aerospace company, and decided to do ecology, and then returned to engineering through glaciology , starting in Minnesota. I always go somewhere just because of the place itself, but not because of the drilling. I will do my best to make the drilling go well, because it means that I can still go to some good place. ”

IceCube laboratory at Amundsen-Scott Antarctic Station. It is a particle detector that searches for neutrinos emanating from the brightest astrophysical sources - exploding stars, gamma-ray bursts, black holes and neutron cataclysms. Before him there was an AMANDA detector.

He did not get a degree in glaciology, and he, as he recalls, “very quickly ran out of time when they suddenly called me and said that the University of Nebraska-Lincoln is looking for a person with an engineering degree who is knowledgeable in glaciology. So I phoned them, they took me to work by telephone in the middle of October, and after two weeks I was sitting in an airplane flying on the Ross Ice Shelf .

The Ross Ice Shelf floats on the surface of the sea near the Antarctic McMurdo Station and provides a stable platform for the station’s airfield, the Williams Field. This is the largest floating mass of ice on the planet, comparable in size to France. For the first time Bruce was there in the Antarctic summer of 1977-1978.

The University of Nebraska-Lincoln received a contract from the National Science Foundation to drill a well across the 60-meter ice shelf so that a group of scientists could explore the ocean beneath. The flame jet used in the mining industry for cutting crystalline stone served as a drill . It consisted of two compressors weighing 4.5 tons each, supplying air at a pressure of 70 atmospheres to a modified jet engine — essentially, a giant Bunsen burner — lowered into a well with turbid water, spitting flame and unburned diesel fuel.

"Well," said Bruce, "she rumbles terribly. Lots of noise, a lot of smoke, a lot of dirt. But she drilled the ice shelf pretty quickly. It turned out a hole of about 45 cm in diameter, so that scientists were able to lower their gizmos there and conduct their experiments. "

In the decade that followed, he helped the glaciologist Charlie Bentley of the University of Wisconsin-Madison drill many small holes with hot-water auger - in general, a giant garden hose - in different parts of Antarctica so that Bentley could then throw dynamite into the holes and engage in seismic experiments. He perked up in the complex art of drilling ice cores , in which a hollow drill pipe with smooth inner walls, threading on the outside and sharp teeth at the bottom periodically plunges into ice to cut the segments and pull them up, one meter at a time. He drilled ice cores in Greenland and many places in the Antarctic, including the pole - and also found time to invent high-altitude drilling of ice cores.

By the spring of 1990, Bruce became one of the best specialists. He participated in three dozen drilling expeditions and was the best practical expert in ice drilling in all its forms on the planet. When John Kelly, director of the US Polar Ice Core Ministry, came to Bruce and asked if it would be interesting for a group of physicists to drill a few wells in Greenland to explore the possibilities of building a neutrino telescope at the South Pole, he jumped at the chance. “Of course!” He recalls his words. “This is the most interesting project I’ve heard about! If necessary, I will not sleep and will work at night. ”

In August 1990, Bob Morse, a physicist from the University of Wisconsin, and Tom Miller, a graduate of the University of California at Berkeley, went to Greenland to spend the first ice fishing for muons. Their fishing gear consisted of three photomultipliers obtained by Morse.

The sensor is lowered into the hole in the ice

Bruce prepared the well he drilled last summer. As the wells in the ice collapse due to the pressure of the ice, he drilled it to a depth of 217 meters. Physicists lowered their line there, and carried out the first part of the measurements. Then they decided that they wanted to increase the optical connection between the photomultipliers and ice, and asked if the drillers had any liquid that could be poured into the well. Unfrozen liquids are in short supply at Greenland Heights, but they have huge reserves of butyl acetate used to prevent well collapse. They poured it inside to cover the line, and made repeated measurements.

“I don’t know why it seemed to us that we needed to pull out the line,” says Bob, “but we pulled it out, and suddenly we saw this thick blue slime covering everything. Butyl acetate dissolved wire braid, and painted all the snow and liquid nearby in a beautiful purple-blue color. We wondered if we would even have at least some light to pass through it. We photographed photomultipliers before lowering, and then after lowering, and in the second photo it looks like a large grape fruit ice. I had blue liquid in gloves, in clothes, on face. It was the dye that was used for the cable. Electricity worked, but optically, we were not sure what we had done. ”

The young team of the project AMANDA (Antarctic Muon And Neutrino Detector Array) [Antarctic array of muon and neutrino detectors], which included Tim Miller, Beauford Price, Andrew Westfal, Steve Barwick, Francis Haltzen and Bob Morse [Doug Lowder, Tim Miller, Buford , Andrew Westphal, Steve Barwick, Francis Halzen, Bob Morse], sent a letter to Nature magazine published in September of that year. Francis believes that this “letter launched an experiment,” demonstrating that the idea of ​​using polar ice as a neutrino detector “was still insane, but not too much.”

The letter reads that “the well was filled with butyl acetate, an organic liquid, chosen because of the low freezing point and optical definition”. No mention of blue mucus. “We found the results inspiring, and we plan to conduct more profound experiments at the South Pole in the coming southern summer.”

It is with such obstacles and shortcomings that they conduct scientific experiments. As Bob Morse wrote:
Greenland is a great example of a quick-witted experiment to watch out for the opportunity. Errors were made, and imperfect data was obtained that was still useful, as failure can come in handy with the right approach. This is a small experiment that preceded the project AMANDA, had all the features created later projects AMANDA and IceCube. The successes that came later were obtained only due to the debugging of the placement and data acquisition systems - but this task was not trivial. A rare example of how organizations funded an experiment more trust in data (albeit imperfect) than many experimenters.

Francis adds that "it is clear that we had no idea what we were doing, so this was the real study, right?"

He suspected that “many people had a similar idea, but they understood glaciology better than me, and obviously decided that it would not work. If we really understood what we were doing, we probably wouldn’t do it at all. And, as it turned out, a lot of things that we should have known were wrong. ”

5 MW heating installation at the IceCube rig. Hot water is flowing through the hoses from the heating installation to where ice is being drilled at the moment. The hose used for drilling has a length of almost 3 km, and is wound on a large coil in the center.

In the lectures he reads today to young scientists, he sometimes uses the early days of the AMANDA project as an example for an aphorism: “Do not read books, do business. It’s best to be ignorant lucky. ” Original discoveries are usually made by young people who are not familiar with generally accepted knowledge. He believes that he was able to do something original at an age well past 40 just because he felt “young again,” in the sense of being naive. "Only when you are still an ignoramus and have not read all the books, can you do something original and new."

He entered the world of experimentation, not driven by the unspent logic of the theory. Experiments have not only to take into account many practical and strategic aspects - sometimes it is best to stop thinking for a moment and just do something.

If he had read an authoritative textbook on the optics of ice and water, he would have “learned” that the absorption length of blue light in pure ice — the distance at which about two-thirds of the light is absorbed — is about 8 meters. And then it would all be over. They would return photomultipliers and go home. If the Cherenkov radiation was actually absorbed at such a short distance, then it would take about 2 million photomultipliers to fill a cubic kilometer of ice, and only about $ 6 billion would have been spent on them. Fortunately, the book was very wrong. They obtained an approximate value of 18 meters from the Greenland data, and although this figure also turned out to be incorrect, it was a step in the right direction.

A few years later, when they were still trying to understand the ice, but had already received signs that the absorption length was actually even more than 18 meters, the library from Madison mistakenly delivered books to someone else's office in Francis's office. Naturally, he began to look at them, and when he reached the information about the eight-meter absorption length, he felt a chill sneaking up his back.

Southern spring of 1991 Bob Morse, Bruce Kochi, Steve Barwick and Tim Miller traveled south to conduct the first drilling for AMANDA. The PICO experiment, which looked for direct evidence of the existence of dark matter, also sent a drilling team to the task, in which Bill Barber was also a tall, good-natured, unruffled and incredibly strong British man.

They wanted to use a hose with a nozzle at the end to spray a parallel stream of hot water, after which the nozzle would simply sink into the melting ice under the influence of gravity. When drilling with hot water, you need a lot of very hot water going under high pressure, and a large diameter hose with good thermal insulation of the walls so that the water stays hot on the way down and transfers as much heat as possible through the nozzle to the ice. True, you need to maintain a balance and let some heat escape through the side walls so that the water does not freeze at the top of the well. Once, Bruce pointed out that just as there are no too large neutrino telescopes, so “there are no too large hot water drills, because the best auger is one that drills a well instantly.” This, of course, is an imaginary drill - delivering an unlimited amount of heat almost instantly - but it conveys the essence: you need a lot of heat and a huge hose.

Bruce knew that their installation, called "Bucky-1", had serious limitations on both parameters. The diameter of the hose was only 2.5 cm, and the heating station, which contained several boilers standing on the street directly on the ice, produced only 0.5 MW of energy. The first hot-water drill that he used on the Ross Shelf used a 2 MW station. “We knew that Bucky-1 had limitations, but we didn’t know exactly which ones, because it was the first time anyone ever tried to drill such cold and deep ice.” He calculated that when they pass 1000 m, the heat leaving due to losses along the length of the hose will exceed the output power of the station. In other words, the bottom of the hose may freeze. He could play different games, trying to keep him from freezing, for example, constantly raising and lowering it to warm the water in the hole just made, but this would require additional fuel, and in general it would be quite difficult to do.

“Hot water drilling is not for wimps,” he says. “We are trying to keep the temperature at least 50 degrees, and this is not always pleasant.”

The project team AMANDA attracted everyone with its bathtubs, which heated water for drilling. While the science foundation did not stop this business, they organized parties in the hot tubs at the drilling site. And it's good that they had fun, because the drilling itself went so-so.

At the second well they were greedy and tried to sink below 1000 m. This led to the worst outcome that could be expected from hot drilling.

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

“Yeah, like a radar tag,” said Bruce.

Bob was sleeping in his James Widge Arctic tent when a drone from PICO, Dave Kestor, stuck his head behind a curtain and whispered that he had bad news. Since one of the three shifts in the camp is constantly trying to sleep, the Summer Camp constantly maintains silence.

"What should we do? - Dave asked. “Should our tools go down there or not?”

“My God, I do not know,” answered Bob. - I think it will be necessary. We have already invested so much in this hole. We must do everything we can. ”

He got out of bed and went in search of Steve Barwick. "I say:" Steve, they have a drill stuck there. " Steve got mad and started shouting - he didn’t know where Them Miller was, so he went to look into each tent at three o'clock in the morning, and yelled with all his might: „Tim Miller? Tim Miller, where the hell are you wearing? Where are you hanging around? “And I thought that now some hefty two-meter worker would just get up and kill Steve. I thought he had a cover. ”

PICO took only two shifts to drill, each of which worked for 12 hours, and the drill was stuck at the night shift. Bruce was in the daytime, and although he still didn’t sleep much while drilling, he walked alongside, stayed up to date, not even on his shift - he was just asleep when trouble struck. And they not only stuck the drill, they also stopped the flow of water in the hose. This is probably the only situation with hot water drilling, from which there is no way out.

“Anyone who has ever drilled hot water has made a mistake at least once in his life and has not given enough heat,” said Bruce later. He decided that they were lucky to reach even this depth.

They tried to pull it out with a Caterpillar D7 bulldozer.

Bob said that “this damn hose was pulled like a string from a violin. He shrank to half his diameter. Only Bill Barber had the courage to go there and stand when the hose was sticking out of this hole, and then take a saw and cut it. And we saw this hose disappear into the hole at the speed of sound, and we heard such a fuse.

And in such a situation, when the end of the drill and a rather large part of the hose disappeared into the well, they followed the advice of the sleepy Bob and lowered the fishing line with the equipment there. For some reason — the hose was stuck, or the well was too narrow — it only traveled 150 m. Then they began to worry that light from the surface could reach the detectors and block any muon signals they could receive. The photomultipliers were extremely sensitive; they worked at the level of single photons, that is, they could detect individual particles of light.

"I looked around and said:" We need to plug the hole. What would shut it up? ”Recalls Bob. - We had asbestos and green garbage bags. Environmentalists would postpone bricks if they found out about it: I started shoving asbestos insulation into bags so that they would gain volume, and threw them into the hole, trying to make a plug from the light. I think I threw three or four in there - as much as I had. "

Experimental physics, with all the flaws and problems.

Mark Bowen is a writer and physicist. He has written for Climbing, Natural History, Science, Technology Review, AMC Outdoors magazines, and has been involved in AMANDA and IceCube projects since 1998. Excerpt from the book "The Telescope in the Ice", 2017.


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