Design and production of the IceCube digital optical module

The first string of 70 in the IceCube neutrino observatory was deployed at the South Pole site in January 2005 and is now taking data. An IceCube string is composed of 60 digital optical modules (DOMs) each of which is an integrated package of a large area photomultiplier tube, high voltage unit, LED flasher calibration board, and embedded digital data acquisition system encased inside a glass pressure housing. The DOM posed a challenging design problem that had to simultaneously meet the extremes of high reliability in a remotely-deployed high pressure and low temperature environment, low power, wide dynamic range from single photon hits emitted by passing cosmic ray muons to tens of thousands of photons from immense electromagnetic showers, and fast time tagging of events to nanosecond precision. In addition the DOM had to be cost effective and reliably producible in quantities of several thousand units. The first year of real DOM production and testing was 2004: 400 DOMs were produced worldwide and tested in special dark freezer laboratories at temperatures ranging from + 25 to - 55 ∘ C . Two hundred and eighty DOMs were sent to the South Pole for deployment and tested there again prior to deployment. Now frozen in the ice, the DOMs are showing exceptionally promising functionality.