FPGA Based Serial and Single-Clock Cycle Pipelined Fast Fourier Transforms in a Radio Detection of Cosmic Rays

Results from various cosmic rays experiments located on the ground level, point to the need for very large aperture detection systems for ultra-high energy cosmic rays. With its nearly 100% duty cycle, its high angular resolution, and its sensitivity to the longitudinal air-shower evolution, the radio technique is particularly well-suited for detection of Ultra High-Energy Cosmic Rays (UHECRs) in large-scale arrays. The present challenges are to understand the emission mechanisms and the features of the radio signal, and to develop an adequate measuring instrument. Electron-positron pairs generated in the shower development are separated and deflected by the Earth’s magnetic field [1], [2], hence they introduce an electromagnetic emission. During shower development, charged particles are concentrated in a shower disk of a few meters thickness. This results in a coherent radio emission up to about 100 MHz. Short but coherent radio pulses of 10 ns up to a few 100 ns duration are generated with an electric field strength increasing approximately linearly with the energy of the primary cosmic particle inducing the extended air showers (EAS), i.e. a quadratic dependence of the radio pulse energy vs. primary particle energy. In contrast to the fluorescence technique (e.g. used in the Pierre Auger Observatory [3]) with a duty cycle of about 12% (fluorescence detectors can work only during moonless nights), the radio technique allows nearly full-time measurements and long range observations due to the high transparency of the air to radio signals in the investigated frequency range.

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