December 8, 2008, South Pole Station -- Tom Gaisser
South Pole IceCube Project
I arrived at the South Pole on November 12 by LC-130 from McMurdo. Jerry Marty, the current National Science Foundation representative here, was on the same flight. Jerry has been coming to the South Pole nearly every year since 1974. Most recently, he has been in charge of construction of the new South Pole Elevated Station that was dedicated in January this year. Jerry knows the pilots and is often invited to sit up in the cockpit during the flight to Pole. He very kindly delegated this privilege to my IceCube colleague Jim Haugen for the takeoff and to me for the landing. I took this picture about an hour before landing at the South Pole, as we crossed the last of the Trans Antarctic Mountain range.
I am here to work on the IceCube project. The primary goal of IceCube is to detect neutrinos of high energy and to look for interesting sources that produce them. Because neutrinos are weakly interacting they are very hard to detect. For this reason, IceCube is very large so that it can measure a reasonably large sample of the elusive neutrinos. IceCube uses the two mile deep, clear Antarctic ice sheet as a target to convert a small fraction of the passing neutrinos into charged particles that produce light as they move through the ice. To detect the light and reconstruct the trajectory of the neutrinos, IceCube uses an array of thousands of detectors buried in more than a mile down in the ice. There are 60 optical modules on each cable with 50 feet between nearest neighbors. The distance between neighboring cables is about 400 feet.
On the next page I show a drawing of IceCube. Each line represents one cable. The darker dots between 1400 meters and 2400 meters each represent a digital optical module (DOM). The Eifel Tower is shown for scale. The dots on the surface represent IceTop stations. Each station has two tanks filled with clear ice, and each tank has two DOMs embedded in the ice. IceCube is now half finished with 40 "strings" of DOMs and 40 IceTop stations. This season we are installing 16 more strings and 19 surface stations. The DOM consists of glass pressure vessel that contains a sensitive photomultiplier tube (PMT) that can detect individual photons of light, a computer and an atomic clock. Each clock is synchronized to a single GPS clock on the surface. The computer digitizes the profile of each signal, provides a time stamp and sends the data to the surface. Left: artist’s drawing if the IceCube array. Below: drawing of a digital optical module.
Most of the events that IceCube sees are produced by the high-energy portion of the cosmic radiation that continually bombards the atmosphere. Protons and atomic nuclei of sufficiently high energy produce cascades of secondary particles that reach the ground as well as high-energy muons that penetrate to the deep part of IceCube. The way IceCube finds the one in a million of neutrinos in this background of cosmic-ray muons is by finding events that move upward. Such events can only be from neutrinos that have passed through the Earth and happened to interact below or inside IceCube to produce an upward-moving event.
I have been interested in cosmic rays and neutrinos throughout my career, so it is really exciting to be able to have a part in building IceCube. Although its primary goal is to find high energy neutrinos from distant astrophysical sources, IceCube, with its surface component IceTop, is also a fine cosmic-ray detector. The main role of our group at the University of Delaware is construction and operation of IceTop. I will write more later about how IceTop works as a cosmic-ray detector, but for now I want to say a little about the choreography of the construction season and how IceTop fits in.
The top priority of the season is to drill holes and deploy the deep cables and DOMs of the neutrino telescope. This is a 24 / 7 operation, with three overlapping shifts of drillers and the on-ice drill leader, Dennis Duling. There are four buildings with hot water heaters and a set of high pressure pumps that force very hot water under high pressure to make the holes in the ice. The main reel holds a 2.5 km long length of hose. The IceTop work place is one of the buildings in the “drill camp” because we get our water to fill the tanks from the main reservoir of the drill system.
This picture by Jim Haugen shows the drill tower with the main hose at the start of drilling the first hole of the season at station 18. The steam is from the hot water heaters in the drill camp.
Two IceTop tanks at station 27 being filled from our water transport tank. Hermann Kolanoski is tending the fill hose and Jonathan, the fork-lift driver is standing behind Hermann on the edge of the pit. The building in the background is the IceCube Lab. Tanks are set below grade so that after the water freezes at the end of the season their tops will be flush with the surface. Between the tanks is the surface junction box which contains the connections to the DOMs in the tanks. Eventually it will also contain all the connections to the DOMs on the down-hole cable. Photo ”" T. Gaisser.
We work closely with the drillers to coordinate filling and deploying our tanks with their operations. During my four-plus weeks here I am on-ice lead for IceCube, which gives me the responsibility and opportunity to be aware of all the operations involved with drilling, pulling cables and testing and deploying DOMs in the deep ice as well as our IceTop deployments.
Left: Dennis and Tom discussing where to put the water transport tank at Station 36; Right: Dennis and Jeff Cherwinka discussing where to set the drill tower for Hole 36. Photos - Hermann Kolanoski.
Station 36 will be the third hole of the season. We were filling the tanks at this station on Saturday at the same time the drill tower was being moved into place in preparation for drilling. The IceTop tanks are between the tractor with our water transport tank on the left and the drill tower on the right. The IceCube Lab is in the background. So far, two holes have been drilled and one deep cable of DOMs deployed. Photo ”" T. Gaisser.