Study on two-cell rf-deflector cavity for ultra-short electron bunch measurement

We have been developing an S-band Cs-Te photocathode rf electron gun system for various application researches such as pulse radiolysis experiments and laser Compton scattering experiments at Waseda University. These researches demande for high quality and well controlled electron beam. In order to measure the ultra-short electron bunch, we decided to use rf-deflector cavity, which can convert the longitudinal distribution to the transverse. With this technique, the longitudinal bunch profile can be obtained as the transverse profile on the screen monitor. We used the 3D electromagnetic field simulation codes HFSS for designing rf-deflector cavity and GPT for beam tracking. The cavity has two-cell structures operating on π-mode, standing wave, dipole(TM₁₂₀)mode at 2856 MHz. We have confirmed on HFSS that two-cell rf-deflector cavity can produce 660 G magnetic field per cell on beam line with 750 kW input rf-power. This field strength is equivalent with our target, which is 100 fs bunch length measurement at 4.3 MeV. In this paper, we will present the cavity structure design, and the measurement results of manufactured cavity.