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Pierre Auger Observatory

Digital electronics for the FD system

The Pierre Auger observatory intends to measure the energy spectrum, the arrival direction, and the isotope composition of primary particles above 1019eV. The very low integrated particle flux of only 1 event per km2 and century for energies above 5 1019 eV demands a very large detector area. The observatory is a hybrid system consisting of 1600 surface detector (SD) stations and an independent fluorescence detector (FD) system. The SD measures the lateral distribution of secondary particles using water Cerenkov detectors equally spaced on a grid over an area of more than 3000 km2. The FD system observes the longitudinal development of the shower profile through 4 optical detectors - called "FD eye" station. During clear dark nights each eye collects the fluorescence light emitted isotropically along the shower track as a time sequence of light. The design provides a central FD eye station with a 360 degree field of view and three perimeter eyes with 180 degree field of view looking towards the center of the SD array. IPE is responsable for processing of the digital data, the detection of fluorescence light in the image of a camera and provides the software for readout of the digital electronic.

Concept of the digital trigger system

All functions of the digital electronic are implemented in reprogrammable FPGA logic in order to achieve high exibility, cost-effectiveness and ease of maintenance. The high data rate from the sampling of the PMT signals is reduced through a multilevel trigger system:

Trigger level Reduction method Rate (Hz)/ Unit
Pure data none 107 per pixel
First Level Trigger (FLT) Filtering and threshold 100..200 per pixel
Second Level Trigger (SLT) Pattern recognition 0.1...1 per mirror
Third Level Trigger further criteria << 0.02 per eye


Dr. Matthias Kleifges,, Tel.: +49 7247 82-3540

The first FD building at Los Leones
The frontend electronic for the FD camera
First level trigger electronic (left) and analog electronic build by INFN, Turino (right)
Screen shot of the diagnostic program showing a cosmic event

Andreas Kopmann,, 06.09.2002
Institute of Data Processing and Electronics, Research Center Karlsruhe
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Forschungszentrum Karlsruhe, Member of the Hermann von Helmholtz-Association of National Research Centres, Germany