A FADC-based data acquisition system for the KASCADE-Grande experiment

We present the design and first test results of a new FADC-based data acquisition (DAQ) system for the Grande array of the KASCADE-Grande experiment. The original KASCADE experiment at the Forschungszentrum Karlsruhe, Germany, has been extended by 37 detector stations of the former EAS-TOP experiment (Grande array) to provide sensitivity to energies for primary particles from the cosmos up to 10¹⁸ eV. The new FADC-based DAQ system will improve the quality of the data taken by the Grande array by digitizing the scintillator signals with a 250 MHz sampling rate. The signals of each of the 37 detector stations are continuously recorded using cascaded 12-bit flash analog-to-digital-converters (FADCs) located on custom made digitizer boards at each station. The digitizer boards feature a self-triggering mechanism, initiating the data transmission to the Grande DAQ station using programmable thresholds, a time stamp mechanism and optical data transmission. The control logic is implemented using field programmable gate arrays (FPGAs). Five optical receiver and temporary storage modules receive the data from up to eight stations each (at an approximate rate of 2.5 MB/s per station) and transfer them into the memory of one of five PCs via a customized PCI interface card. Running on a master PC, the data acquisition software searches for coincidences in the time stamps, incorporates triggers generated by the other KASCADE-Grande components and builds air shower events from the data of the individual stations. Completed Grande events will be sent to the central DAQ of KASCADE-Grande at an approximate rate of a few air shower events per second. Two Grande stations have been equipped with the FADC-based data acquisition system this summer (2004) and first data are shown. By the beginning of 2005 completion of the full system is anticipated.