DDS-based multiple frequencies generator for the RF systems at INFN-LNS

On the latest accelerated beams, all the RF systems, the axial buncher [2], the three RF cavities of the superconducting cyclotron [7] and the high energy chopper [2], have been driven from the DDS generator. The phase stability, between these components of the RF System [3], is stable in order to ensure the stability on the extracted and choppered beam. With this new generator based on the Direct Digital Synthesis, we would like to achieve the same stability on the final beam of the old RF source generator system. The main reason for following this new technique in the synthesis of the RF sinusoidal signals is given by the future introduction along the extraction beam line of the Chopper 500 [2]. This new beam chopping system will replace the present High Energy Chopper. The goals of the new chopper system are: the separation time between the accelerated beam bunches of 100÷200 ns and to reduce to 0.5 ns the length of the single bunch. At the moment we have this separation up to 200 ns, with the length of the bunch no less than 1 ns. In order to reduce this bunch length and maintain the same separation time, we ought to drive the new chopping system, the Chopper 500, choosing a non integer multiple harmonic of the fundamental RF cyclotron. The old RF source generator develops integer multiple frequencies, starting with the lowest RF, which generally belongs to the High Energy Chopper. The DDS frequencies generator allows the generation of sinusoidal output signals, highly stable in frequency, phase and amplitude respectively, without any problem between integer or non integer harmonic. To choose the output frequencies you simply address a “new tuning word” by a personal computer via a parallel port to the core of the system. This is a commercial electronic component: the AD9852 on its own evaluation board [4]. We have three boards capable of DDS-based multiple frequencies generator for the RF systems at INFN-LNS Antonio Caruso, Luciano Calabretta, Antonino Spartà, Fabrizio Speziale, Emilio Zappalà, Xu Zhe