IceTop, the Air Shower Array of IceCube

A lot of people have asked me what we are doing at the Pole. Some of you already know about the IceCube project and others don't. Simply put, we are building the worlds largest neutrino telescope.

What's a neutrino telescope? Aneutrino is a unique particle that is very illusive. It rarely interacts with anything. It is not effected by magnetic fields or things like planets it its way. Most neutrinos pass entirely through the earth. For that reason, we need a really big detector to look at the few neutrinos that happen to interact with the Antarctic ice. The cool thing about neutrinos is, because they are not effected by magnetic fields or bodies of mass, they point directly back to the source that created them. Other cosmic ray particles are influenced by magnetic fields and spin and curve their way here so it is harder to tell about their origin.

The IceCube detector will consist of 70 to 80 detector strings taking up a cubic kilometer of ice. A hole is drilled 2,400 meters deep into the 2 mile deep South Pole ice cap using a five million watt hot water drill. The first detector on each cable is at a depth of 1,400 meters and the deepest detector is at 2,400 meters. At that depth the ice is very clear from the extreme pressure. I've attached a picture to show you the scale of this project.

DOM ready to be deployed

The detector is called a Digital Optical Module or DOM. Each DOM is a sophisticated computer and data acquisition system. At the heart is a photo multiplier tube. It is a device sensitive enough to detect a single photon of light. As a neutrino passes through the ice it occasionally slams into a molecule of ice. The collision produces other particles (muons) that produce a small flash of light as they pass through the ice. This Cherenkov light is detected by the DOM. The DOM stores information about the flash of light and stamps it with a precise time measurement. The information is sent to the surface to the IceCube Lab. Computers at the surface collect the information along with the information from all of the other DOMs. The path of the particle can be reconstructed and the scientists can look back and see where it came from. Maybe it came from an exploding star or a black hole.

Drill Camp Drill Tower
IceCube Drill Camp (left) and Drill Tower (right)

Building a detector of this size is no small chore. The University of Wisconsin first had to design and build a hot water drill that could survive the tough conditions at the South Pole. Then it had to be sent here. Everything is flown into the South Pole by C130 (Hercules) military cargo aircraft on skis. The Drill Camp was then set up and assembled on the ice. The first year things had to be tested and tuned for optimum performance. The first season (Nov - Feb 2004/05) only one hole was drilled and one string of detectors deployed. Still a successful year. The second season eight more strings were deployed. This season the seventh string will be deployed tonight and several more are planned before the station closes in Feb. Thus far, there are a total of 16 detector strings in the ice. It will be several years before the project is completed.

Fern Drill
Fern Drill

The first 50 meters is drilled using the fern drill. It circulates hot water through the copper coils of the fern drill "Carrot". It is lowered slowly and melts its way through the snow layers to the ice. Then the main drill is placed in the hole and hot water is sprayed at 200 gallons per minute to drill through the deep ice. A return water pump returns the water from the hole back to the drill camp tanks to be heated again. The drill camp uses JP8 jet fuel brought in by the C130s to heat the water for the drill. (And you thought gas was expensive!)

I was selected as a deployment team member for string six of this season. It is fascinating to look down into a hole in the ice and think that it goes down for nearly two miles. I was excited when we lowered the first DOM into the dark hole. A stack of weights guides the first DOM down the hole. As we all posed around the 60th DOM placed on the string, 12 hours later, I was not so skeptical about the depth of the hole! It was an exhausting effort and not without its share of challenges. It was a successful deployment. Only 55 to 65 more to go!

Down And Down We Go...
Drill Down The Hole DOM Down The Hole
After the drill has done is job (left), the DOMs are lowered one by one into the ice (right)