Ultrashort bunch duration measurement using S-band RF deflector in UED system at KAERI

As demanding the ultrashort bunches for the pump & probe experiments to investigate ultrafast phenomena occurring at atomic size level, the diagnostic tools should be developed to measure. by measuring the electron diffraction pattern directly. We have developed an S-band RF deflecting cavity working on $\mathrm{TM}_{120}$ mode to measure the femto-second bunch duration of electron beam in UED (Ultrafast Electron Diffraction) system at KAERI. In this conference, we will present on design, fabrication and experimental performance of the deflecting cavity. The estimated temporal resolution of RF deflector, operating with the deflecting voltage of 1.5 MV and the drift length of 1.7 m, is 50 fs. The electron beam with 3 MeV and 1.88 pC, electron bunch duration has 67 fs in rms, which is well agreed with the simulation results.