The Telescope in the Ice

by Mark Bowen

  As for Francis, as important as gustatory considerations may have been, the quality of the research and teaching environment came first. As Dave Cline has observed, he fit perfectly into the Madison picture. He got tenure almost as fast as Cline did, within two or three years.

  * * *

  Francis was still pure in the watershed year 1987, sixteen years into his American “visit,” when the three underground detectors sensed the neutrinos from Supernova 1987a. He’d been dabbling in the dark side since his visit to Hawaii seven years earlier—he and Tom Gaisser of the Bartol Research Institute at the University of Delaware wrote an influential paper on cosmic rays in 1984—but he still worked mainly in particles. And he continued to travel widely, visiting collaborators, giving talks, picking up pollen on his knees, and spreading it around.

  In the fall of that year, he was invited to speak to the physics department at the University of Kansas. He guesses that the topic was “cosmic accelerators and the (now defunct) evidence that Cygnus X-3 emits mysterious particles.” He might well have talked about Supernova 1987a, and considering what happened next, he undoubtedly mentioned DUMAND.

  The Cygnus story demonstrates, incidentally, how science can be advanced even by false leads. In 1983, groups from Kiel, Germany, and the University of Leeds presented evidence that Cygnus X-3, an X-ray source in the constellation Cygnus, was emitting very high-energy gamma rays. Subsequent studies proved these studies wrong, but the “damage” had been done. Some of the more adventurous members of the particle physics community, driven in part by the fact that their field was just entering the desert (the W and Z were discovered that same year) began migrating into cosmic rays. This led naturally to progress, and in 1989 a specialized telescope in Arizona detected the first true high-energy gammas from the Crab Nebula. Gamma ray astronomy has since flourished, and dozens of gamma ray sources have been discovered in the meantime. And since gamma ray and neutrino astronomy borrow many of their techniques from particle physics and share a lot of science with it as well, their ascendance has given rise to a new field that combines astronomy and cosmic ray physics. It’s known as either particle astrophysics or astroparticle physics, take your pick.

  Anyhow, it so happened that an unusually versatile scientist by the name of Ed Zeller was sitting in the audience in Kansas. Zeller had been trained as a glaciologist, also had an appointment in physics, and was an old Antarctic hand. During the discussion after Francis’s talk, he mentioned a feasibility study that was taking place at the Soviet Union’s Vostok Station in Antarctica, in which a small array of radio antennae was being used to “listen” for neutrinos interacting with the ice. It was known as RAMAND, for Radio Antarctic Muon And Neutrino Detector, and it was being led by Igor Zheleznykh, the second of Moiseĭ Markov’s neutrino lieutenants. RAMAND had not detected any neutrinos; in the end, it never would.

  The radio method had been conceived by the Russian physicist Gorgen Askaryan in 1961. It is based on the fact that at very high energies both muon neutrinos and electron neutrinos will generate cascades, and these cascades are essentially sparks consisting of millions of positrons and electrons, which produce jagged radio pulses.

  “My interest peaked with [Zeller’s] comment that the Russian physicists had been unable to compute the power in the signal,” Francis later recalled. “With an enthusiasm reminiscent of graduate electromagnetism, [two collaborators] and myself solved the ‘hardest Jackson problem ever,’ using superior computer power not available to our Russian colleagues.” (J. D. Jackson’s textbook, Electrodynamics, provides a bittersweet rite of passage for many a physics student.)

  The problem was interesting, but the answer was disappointing. Francis, John Learned, and Bartol theorist Todor Stanev later estimated that with the technology of the day, even if RAMAND had been monitoring a cubic kilometer of ice it would only have detected about one neutrino every hundred thousand years.

  Francis believes theorists write two kinds of papers: “the ones they really believe in, that they feel passionately about,” and others simply to show how smart they are. This one fell in the showing-you’re-smart category. He wrote it, put it in “the stack that you submit every year to the university for your salary,” and moved on.

  But Zeller’s remarks prompted him to put two and two together on another front. He was quite aware of DUMAND, of course, and now he had heard about neutrino detection in ice. “You don’t have to be a genius,” he says. “Eventually you’re going to hit the idea: if the Hawaii stuff doesn’t work in water, maybe it works in ice. And forget the radio detectors; do just what [DUMAND does].… That was all there was to it.”

  He sent an e-mail to his theorist friend Sandip Pakvasa in Hawaii, asking him to ask John Learned if he’d “ever thought about whether you can do this in ice.”

  He and Learned exchanged frantic e-mails for several weeks. They queried Zeller, who assured them (naïvely in retrospect) that the deep ice in Antarctica ought to be clear. And the more they considered the idea, the more compelling it became: Ice would be free of the dissolved radioactive potassium in natural bodies of water, which gives rise to a confounding background luminescence. The detectors would remain stationary; they wouldn’t slosh around with changes in water currents. Neither would they accumulate sediments, which was also a worry so close to the ocean floor. And finally, as at Lake Baikal, the ice would provide a stable platform for deploying the instrument.

  * * *

  But Francis wasn’t ready to take the plunge into experimentalism quite yet. He still thought of himself as a theorist. He was happy to write a few papers about “DUMAND on ice” and present the idea at some conferences, but that’s as far as he was willing to go. Learned, on the other hand, was at the height of what might be called his neutrino megalomania at that point in time. He was still leading DUMAND, he was a member of IMB, he was about to join the successor to Kamiokande, Super-K, and he had another line in the water in Arkansas. Nevertheless, he was more than willing to take a shot at building a second DUMAND on the bottom of the planet.

  There are many political angles to doing science in Antarctica. One is that the continent is governed by a surprisingly enlightened international treaty, which encourages science and environmental protection but prohibits military activity and territorial claims. For this reason, Learned’s primary funding source, the Department of Energy, isn’t particularly welcome, since it is deeply involved in the U.S. nuclear weapons program. The purely scientific National Science Foundation (NSF) oversees the entire U.S. presence in Antarctica.

  The Madison connection crops up again here. For as it happened, John Lynch, the administrator in charge of Polar Aeronomy and Astrophysics at NSF, in both polar regions, north and south, knew John Learned and Francis Halzen well. He had been a graduate student in the Madison physics department back in Learned’s post-doc days and Francis’s early days as a professor. He was also a contemporary of Bob Morse—the two had met on their very first day of graduate school. Perhaps most importantly, Lynch had been a regular at the 602 Club, the bar where Dave Cline, Bob March, and the rest of the CCFMR gang held court.

  As Lynch remembers it, Learned sent him an e-mail “with no capital letters in it, demanding that I, you know, let him drill six hundred holes five thousand feet deep at South Pole, next year.” Although he dismissed this half-baked request out of hand, he appreciated the concept well enough to show the e-mail to his boss, Peter Wilkness, director of the foundation’s Office of Polar Programs, whom he describes as a “genuinely larger than life guy,” who “just loved big things.”

  In May 1988, Learned got more formal, but not formal enough. He sent Lynch an eight-page letter of intent, based on a paper he and Francis had written for a cosmic ray conference that would take place, in Lodz, Poland, in September.

  Francis observes that “research is when you don’t know what you’re doing.” The most naïve remarks in this paper relate to the ice: “A crucial question is how deep we must go to obtain clear
, bubble free ice because optical scattering from bubbles can ruin … muon detection.… It appears, based upon conversations with Prof. Edward Zeller of the University of Kansas that we will obtain good optical clarity below about 150 meters near the pole, but that we may have to go below 500 meters to find bubble free ice.”

  An insight that has held up, on the other hand, was that it would be much less expensive to build a neutrino telescope in Antarctica, surprisingly enough, than virtually anywhere else on the planet, assuming a well-equipped base nearby. Demonstrating a charming lack of political savvy, Learned even suggested that the polar project would be “an order of magnitude more cost effective” than his own project, which was already beginning to founder in the warm waters of Hawaii.

  Learned figured the Antarctic project would attract collaborators from other underground neutrino projects, and “given an acceptable political climate … that our Soviet colleagues would want to participate as well.” Indeed, a few months after he wrote these words, he received a telex from his friend Moiseĭ Markov indicating that “Prof. G. I. Marchuk, President of the Academy of sciences of the USSR … considered this suggestion as interesting.”

  It’s too bad the Russians didn’t get involved, since they would have brought an extensive knowledge of ice to the table. (Wherever there is ice, one will tend to find Russians.) Markov’s telex contained remarks that could have saved the soon-to-be-born AMANDA collaboration years of effort and anxiety, had they been aware of them. Based on the analysis of a 2.2-kilometer-deep ice core that the Russians had drilled at their Vostok station, Markov pointed out that there were “only sporadic bubbles in perfectly clear ice at 1300–1400 meters, so the holes in ice for [phototubes] have to be rather deep”—an insight that would prove dead-on.

  At the end of his letter of intent, Learned requested $100,000 for the upcoming Antarctic season, which was about six months away. In a friendly response, Lynch and Wilkness turned him down.

  Learned’s involvement came to an end when the Department of Energy told him he had to make a choice (although that may be a polite way of putting it). “Basically, I was told by the DOE that I had better stick to—I had to choose between DUMAND and playing these other games,” he says.

  * * *

  One of the first signs that a field is gaining momentum is when conferences develop around it. And the first regular conference dedicated to neutrino astronomy was one of the most civilized one can imagine. It was conceived by Milla Baldo Ceolin, an elegant, brilliant, and beautiful woman, who was in fact the first woman ever to become a professor of physics in Italy. She was Galileo Professor at the University of Padua. There was a Madison connection there, too: Milla, as she was widely known, had begun collaborating with Jack Fry when he had made his early shift to the accelerators in the 1950s.

  Until it became more popular and started focusing on things besides neutrino astronomy, this was Francis’s favorite conference, and he’s been to a few. It was held in the Istituto Veneto di Scienze, Lettere ed Arti in Venice, in noble sixteenth-century halls once graced by Galileo himself. At first, it was very small and by invitation only.

  “In the early Venice meetings we just gathered in a room at the Palazzo Loredan, the smaller building of the Academy,” Francis writes. “Everybody was working on neutrino telescopes; we were there to discuss and help each other—we knew this was going to be difficult.… The meetings were small and I remember the room very well. There was a small transparency projector with the screen a foot from Tintoretto’s Madonna col Bambino.”

  Milla may also have had a civilizing effect upon the competitive men in the field. Francis says that her concept for the meetings was that “with mutual help we could all succeed.” At a meeting in the early nineties, for example, by which time he was engaged in AMANDA, he remembers asking a member of the DUMAND collaboration about the computer simulations they had developed for their instrument, and the response was simply to give him the code. This was a shocking act of generosity to someone accustomed to the sharp elbows in particle physics.

  By the time of the first Venice meeting in 1988, DUMAND on ice had attracted the interest of Bob March, who was already working on the watery version. He delivered a paper, co-written with Learned and Halzen, entitled “Neutrino Detection in Clear Polar Ice.” His literary flourish is evident in the prose.

  One might call the detector to be described in this talk “Solid State DUMAND.” …

  It must be emphasized that this is a “Dio Volente” detector, for to make it feasible three conditions must be met that are beyond our control:

  A natural body of clear ice, of area at least tens of thousands of square meters and thickness a few hundred meters, must exist somewhere within a kilometer or so of the surface;

  The light transmission of the ice in the Cherenkov band [blue] must be comparable to that of pure water, with attenuation (absorption and scattering) lengths of tens of meters;

  The ice body must be situated near an existing permanent research station, for the cost of constructing, maintaining, and supplying a base would be prohibitive.… The third condition effectively limits the choice of sites to the USA’s South Pole Station and the USSR’s Vostok Station.…

  In summary, this is a detector that requires a number of happy accidents to make it feasible. But if these should come to pass, it may provide the least expensive route to a truly large neutrino telescope. Exploratory studies may begin at the South Pole within the next few years.

  Francis was now becoming passionate about this project. With Learned out of the picture, however, he needed to find a collaborator on the experimental side in order to move it along. The obvious choice would have been March or one of his CCFMR colleagues, so Francis would occasionally ask them if they’d like to do something more than just write another paper. “After a while,” he says, “whenever I showed up on the experimental floor of the building, people ran for their offices and closed the doors. You know, they just thought I was crazy.… The one exception was Bob Morse.”

  * * *

  Bob was the perfect man for the job, for a couple of reasons. For one, he specialized in getting new projects off the ground. For another, he had been one of the earliest defectors from the accelerators to particle astrophysics. As he remembers it, at about the same time he joined Dave Cline and Carlo Rubbia on their HPW fiasco in Utah, “Jack Fry and Ugo Camerini convinced Dave that we ought to go into the gamma ray astronomy business. And I thought, ‘Great!’ So off to Hawaii, off to Mount Haleakalā!

  “One of the things I’m accused of is that I’m fast out of the gun; I love to start new things, but I’m never around to help finish them up when all the messy details come around. And I think that’s probably a quasi-legitimate indictment. I really do love planning the new things and getting stuff laid out and getting into the ground work and stuff. And so … Jack Fry came up, and like all good salesman he convinced us that there were probably stars out there … that were putting out lots of high-energy, pulsed—that was the magic word here, pulsed—gamma rays.”

  The gamma ray telescope that the CCFMR group erected on Mt. Haleakalā was the first particle astrophysics experiment of any kind to be placed among the more traditional telescopes on the summit of this 10,000-foot volcano. Unfortunately, however, like HPW, it didn’t work out. Camerini and Cline went in with the arrogant attitude that they could scoop the astronomers by employing some tricks from the accelerator repertoire to detect what they assumed would be periodic pulses of gamma rays from sources that emitted other periodic signals, such as X-ray pulsars, and that the data would roll into their laps like coins from a slot machine. About ten years later, when the first true high-energy gammas were detected from the Crab Nebula, it turned out that they weren’t periodic, and it wasn’t until 2008 that a more sensitive, second-generation instrument finally detected pulsed gammas from the pulsar at the center of the Crab. So the particle physicists got a lesson in astronomy, rather than vice versa.

  But the
side benefit of Haleakalā was that it led Bob Morse to the South Pole. He and his friends soon realized that the equator wasn’t a great place to look for periodic signals, because other periodic effects complicated the measurement: the daily cycle of the Sun and the rising and setting of the very stars they were trying to observe. Basically, it’s more difficult to measure one periodic signal when it’s riding on top of another, so these diurnal cycles increased the noise.

  The South Pole experiences only one very long day a year. The Sun rises and sets at the equinoxes, on about September 21 and March 21, so for about six months it’s below the horizon and won’t complicate things. The stars in the southern sky don’t rise and set either. They describe circles in the sky, centered on the zenith; they’re always in view, although they’re hard to see in summer when the Sun is up. If you set up your telescope to track a star, therefore, you can keep it in sight all winter long, barring clouds, blowing snow, and the spectacular auroras at the pole, of which there are many. The two main complications at Haleakalā don’t come into play.

  So, sometime in the late 1980s, Bob began talking to his friend John Lynch at NSF about trying the Haleakalā idea at the pole.

  * * *

  Martin Pomerantz, the recently retired director of the Bartol Institute, was by then already known as the father of South Pole astronomy. He’d been the first person to do any kind of astronomy there, and he was a great proponent of the pole’s unique advantages for certain kinds of observation.

  The South Pole resembles an ocean, except that it’s white and you can walk on it. The surface of the ice is about as high as Haleakalā, 9,300 feet, owing to the fact that the East Antarctic Ice Sheet is about that thick there. It’s dark all winter, the same stars are always in view, and owing to the incredibly cold temperatures, the air is extraordinarily dry. This makes it nearly transparent to infrared light, so the pole is particularly well-suited to studies of the cosmic microwave background. It’s also an excellent place to observe cosmic rays, because charged particles like to travel along magnetic field lines, so they’re steered by the Earth’s magnetic field to the north and south magnetic poles. The auroras australis in the south and borealis in the north are simply the light given off by cosmic rays as they hit the polar atmospheres.