IceTop, the Air Shower Array of IceCube
Cerenkov light When charged particles travel in a medium (e.g. ice) with speeds faster than the speed of light in that medium, they emit photons. This effect makes cosmic rays visible for our intruments. The Cerenkov effect can be compared to the sonic boom which is caused by objects moving faster than the speed of sound in e.g. air.
DOM Digital Optical Module. These are the key instruments of IceCube. A DOM registers the faint Cerenkov light pulses thus making cosmic rays visible for us. It consists of a photo multiplier and the necessary electronics to register, process, and digitize the signal. In addition, it also records the GPS time.
GPS Global Positioning System. The GPS is a satellite based positioning system that also serves as a precise time reference.
Photomultiplier A classical detection instrument for light sources. In its basic version, it is a vacuum tube with an entry window for the light signals and an amplifier circuit inside. Light hitting the window causes electrons to be emitted via the photo electric effect. These electrons are accelerated and amplified inside the tube. This way, even single photons can be detected!