Measurement of bunch length and temporal distribution using accelerating radio frequency cavity in low-emittance injector

Abstract

We demonstrate an experimental methodology for measuring the temporal distribution of picosecond level electron bunch with low energy using radial electric and azimuthal magnetic fields of an accelerating (TM01 mode) radio frequency (RF) cavity that is used for accelerating electron beams in a linear accelerator. In this new technique, an accelerating RF cavity provides a phase-dependent transverse kick to the electrons, resulting in the linear coupling of the trajectory angle with the longitudinal position inside the bunch. This method does not require additional devices on the beamline since it uses an existing accelerating cavity for the projection of the temporal distribution to the transverse direction. We present the theoretical basis of the proposed method and validate it experimentally in the compact-energy recovery linac accelerator at KEK. Measurements were demonstrated using a 2-cell superconducting booster cavity with a peak on-axis accelerating field (E-0) of 7.21 MV/m.