Electronics and Data Acquisition System in the HiRes Prototype

The Hires Prototype is the second generation Fly's Eye type detector built for the observation of the atmospheric showers produced by ultra high energy cosmic rays ( Bird et al, 1993 ). It is being operated with 14 detector clusters. Each cluster consists of 256 individually analyzed photomultiplier tubes ( PMT ). The 256 PMTs are divided into 16 groups called subclusters. Each subcluster forms a 4x4 block of adjacent PMTs. The task of the electronics and data acquisition system is to filter out the night sky background light, identify the extensive air shower nitrogen fluorescence track, and measure the intensity and timing of each PMT which observes a shower track. The minimum dynamic range and the accuracy of the time and charge measurement are constrained by the desired detector aperture and energy sensitivity range. The system must also be able to process the data and background triggering rates without incurring excessive dead time. These requirements have been met in the Hires prototype by our data acquisition system as described in this paper.