Measurements of Microbunch Energy Spectra on a S-Band Electron Linac

A method was developed to measure with high resolution the energy spectrum of electron microbunches, produced by a S-band Linac. The electron beam is deflected by an analysing magnet and collected on the inner conductor of a fast coaxial target. The signal is analysed by a fast sampling scope which is triggered by a pulse composed of the electron current signal and a residual fundamental which is used as the fine time reference. For a given value of the magnetic field H, those of the bunches having electrons of the corresponding energy contribute to the signal which is displayed bunch by bunch on the scope. Using the manual sweep of the scope and varying H, the intensity variation of each bunch with H is registered. Series of energy spectra of the bunches are shown for electron bursts of 5 and 14 ns. These measurements were performed as part of a feasibility study for the installation of a post-acceleration pulse compression magnet.