Development of a Bunch Frequency Monitor for the Preliminary Phase of the CLIC Test Facility CTF3

In the framework of the CLIC RF power source studies, the feasibility of the electron bunch train combination by injection with RF deflectors into an isochronous ring has been successfully demonstrated in the preliminary phase of CTF3. A new method, based on beam frequency spectrum analysis, was experimented to monitor this scheme. A coaxial pick-up and its read-out electronics were designed and mounted in the CTF3 ring to allow comparison of the amplitudes of five harmonics of the fundamental beam frequency (3 GHz) while combining the bunch trains. The commissioning of the monitor was a successful proof of principle for this new method, despite the short length of the bunch trains and the presence of parasitic signals associated to high-order waveguide modes propagating with the beam inside the pipe.