The AMY (Air Microwave Yield) experiment to measure the GHz emission from air shower plasma

The aim of the Air Microwave Yield (AMY) experiment is to investigate the Molecular Bremsstrahlung Radiation (MBR) emitted from an electron beam induced air-shower. The measurements have been performed with a 510 MeV electron beam at the Beam Test Facility (BTF) of Frascati INFN National Laboratories in a wide frequency range between 1 and 20 GHz. We present the experimental apparatus and the first results of the measurements. Contrary to what have been reported in a previous similar experiment~\cite{Gorham-SLAC}, we have found that the intensity of the emission is strongly influenced by the particular time structure of the accelerator beam. This makes very difficult the interpretation of the emission process and a realistic extrapolation of the emission yield to the plasma generated during the development of an atmospheric shower.