Gallery: The World's Biggest, Iciest Particle Detector
01icecube-video
Construction of the world’s largest particle detector is now complete after 10 years of drilling deeper than a mile into ultraclear Antarctic ice. Called the [IceCube](http://www.icecube.wisc.edu/), the three-dimensional array of sensors can detect neutrinos expelled by some of the universe’s most violent sources, including black holes, supernovas and energetic stars. [Neutrinos](http://stag-komodo.wired.com/wiredscience/2010/06/neutrino-transformation/) weigh hardly anything, so the particles usually travel through matter — including the sun and Earth — without interacting. But every now and then they slam into the cores of atoms to create nuclear particle showers. The events emit faint blue trails of light which IceCube’s 5,160 sensors can track with extreme precision. "About one in a million neutrinos crash into a proton \[in IceCube\]. We’re measuring the energy and the directions of those nuclear reactions to build a neutrino-based map of the sky," said [Francis Halzen](http://icecube.wisc.edu/%7Ehalzen/), a theoretical physicist at the University of Wisconsin-Madison and leader of IceCube. The $100-million neutrino-detection effort is one of the most challenging ever attempted by engineers and physicists, Halzen said. "Nobody would have bet on the success of this project, and rightfully so," Halzen said. “If we knew how complex it would be to build, we may have never started.” In this gallery, take a tour of the world’s biggest, iciest particle detector. *Video: Animations show the drilling of IceCube’s 1.5-mile-deep holes, the completed array of light-detecting sensors and a simulation of a neutrino collision event. Credit: NSF, IceCube/University of Madison-Wisconsin and Chris Bickel.*
02icecubes-firn-drill
The Drills ---------- Engineers drilled each of IceCube’s 1.6-foot-wide, 1.5-mile-deep holes in about two days. They started with a coiled heating element called a firn drill (above) to melt the first 250 feet of snow into water. To burrow through the remaining mile or so of rock-hard ice, they used the Enhanced Hot Water Drill (below). It circulates cold, melted water to the surface, where it’s reheated and pumped back into the drill. [](http://stag-komodo.wired.com/wiredscience/?attachment_id=45844) *Images: IceCube/University of Wisconsin-Madison/NSF*
03hole-in-the-antarctic-ice
Ice Tube -------- Into a finished 1.5-mile-deep tube (above), technicians lower a string of 60 light-sensing modules into the water below. Once frozen, they can never be retrieved. Each string of sensors (illustration below) carries data to a computing center at the surface. [](http://stag-komodo.wired.com/wiredscience/?attachment_id=45846) *Images: IceCube/University of Wisconsin-Madison/NSF*
Robert Schwarz04digital-optical-module
Last Sensor ----------- The last of 5,160 digital optical modules, or DOMs, awaits being lowered into a tube in the Antarctic ice (top). Each DOM contains a photomultiplier tube in its bottom half to detect the blue light of Cherenkov radiation, caused when a particle travels through a material at speeds faster than light (in water, for example, light travels at 75 percent of its speed in a vacuum). The same effect makes water in nuclear reactor cores glow blue. A suite of on-board electronics (below, right) converts analog signals into high-throughput digital signals, and a glass case (below, left) protects everything from the incredible pressures below the surface. [](http://stag-komodo.wired.com/wiredscience/?attachment_id=45845) *Images: IceCube/University of Wisconsin-Madison/NSF*
unknown05icecube-computing-laboratory
Computing Power --------------- A robust computing center (above) sits atop the 86 tubes packed with sensors (below) to process all of IceCube’s data. IceCube detects 220 neutrino events each day, but its computers must filter out 100 million spurious signals to see them. The unwanted events are caused by high-energy particles (that aren’t neutrinos) slamming into Earth’s atmosphere. Each legitimate neutrino event’s energy and direction is recorded, then beamed by satellite to the University of Wisconsin-Madison. Helzen said the best data often comes from neutrinos traveling through the Earth and hitting the ice from below. From the 1970s through the early 1990s, physicists thought building a neutrino detector like IceCube in deep ocean water would be less challenging. Yet after several crucial demonstrations, including the AMANDA experiment that's now incorporated into IceCube, Halzen said his colleagues have come around. "Until we have similar detector in water, it's difficult to compare, but there are efforts underway to build one in the Mediterranean," Halzen said. "Still, there's a deep truth to something I like to say a lot: We can walk on our experiment. Once deployed, you can put a computing center right above the detector on the surface and crunch your data." [](http://stag-komodo.wired.com/wiredscience/?attachment_id=45843) *Images: IceCube/University of Wisconsin-Madison/NSF*
06neutrino-sky-map
Sky Map ------- Even before IceCube was finished, physicists could collect data. The map above represents about 2 years worth of neutrino point sources recorded by 40 strings of sensors. If the hardware holds up like it’s supposed to, Halzen said IceCube could hunt for neutrinos for about 20 years. “Once you put these sensors in the ice, you can never get your hands on them again,” Halzen said. “So far, so good. We’ve only lost a few.” *Image: [Jon Dumm](http://arxiv.org/abs/1012.2137)/IceCube/University of Wisconsin-Madison*
