Commissioning of a Bunch Frequency Monitor for the CTF3 Preliminary Phase

The CTF3 preliminary phase at CERN has demonstrated the feasibility of the bunch frequency multiplication process, by injection of subsequent bunch trains into an isochronous ring. In order toobserve the bunch interleaving at each stage of this process, a new method based on frequency spectrum analysis has been developed. For this purpose, a coaxial RF pick-up and its detection system were designed and mounted in the CTF3 ring, in order to allow comparison of the amplitudes of five harmonics of the fundamental beam frequency (9, 12, 15, 18 and 21 GHz) while combining bunch trains. The commissioning of this monitor was a successful proof of principle for this new method, however with two limitations: the short length of the bunch trains and the presence of parasitic signals associated with waveguide modes propagating with the beam inside the pipe.