XXth International Conference on Neutrino Physics and Astrophysics

Poster Abstract

R.Stokstad for the IceCube and AMANDA Collaborations

The Digital Optical Module - How IceCube will Acquire Data

Large-scale neutrino detectors pose challenging problems for signal processing because of the long distance between the physical sensors and the site at which data from many sensors can be combined to recognize events of interest. It has been possible for AMANDA to use analog transmission (via copper and fiber optic cables) to bring photomultiplier tube signals a distance of ~2.5 km to the surface where timing and digitization can be performed in one central location. IceCube, the km-scale neutrino detector to be deployed near AMANDA in the ice sheet at the South Pole, will have a distributed system with a high-speed digitizer and very stable oscillator located in each PMT module. Power and digital communication signals will be transmitted over copper twisted-pair cable. This system offers improved signal quality, increased dynamic range , and higher reliability. The concept has been developed and tested by the AMANDA collaboration with a string of 40 modules equipped with both digital and analog transmission technologies. Digitized waveforms recorded by a custom integrated circuit (the Analog Transient Waveform Digitizer) at a rate of ~500 megasamples/s are sent to the surface for modules satisfying a nearest-neighbor local coincidence requirement. The 16.8 MHz oscillators used to time-stamp the waveforms are calibrated to an absolute accuracy of 5 ns by sending identical timing pulses up and down at intervals of ~10 seconds. This technique will enable a fully automatic time calibration procedure for IceCube's 4800 digital optical modules. Results obtained with the AMANDA string will be described along with plans for the IceCube DAQ. <

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