Longitudinal electron beam profile measurement using a 2-cell rf deflector cavity

We have been studying a compact electron accelerator based on an S-band Cs-Te photocathode rf electron gun at Waseda University. We are applying this high quality electron beam to a pulse radiolysis experiment, soft X-ray generation, and coherent THz wave generation. In these application experiments, it is necessary to measure temporal distribution and bunch length of the electron beam for evaluating temporal resolution, luminosity, and coherence. Thus we adopted the rf deflector system which has high temporal resolution and the ability to measure them directly. It kicks the electron bunch with resonated rf electromagnetic field. Using this technique, the longitudinal distribution is mapped into the transverse space. The rf deflector has a 2-cell standing wave π-mode structure, operating in TM₂₁₀ dipole mode at 2856 MHz. It provides a maximum vertical kick of 1.00 MV with 750 kW input rf-power which is equivalent to the temporal resolution of around 58 fs. In this paper, we report the details of our rf deflector, the latest progress of the bunch length measurement and future prospective. (author)