Proof-of-Principle Experiment of Velocity Bunching for Ultra-Short Electron Pulse Production

An accelerator test facility, t-ACTS, established at Research Center for Electron Photon Science, Tohoku University, equips an injector consisted with a thermionic RF gun together with an energy filter and a 3 m traveling wave accelerating structure. A long-period undulator has been also installed for provide THz superradiance. Velocity bunching scheme proposed by Serafini and Ferrario is employed for ultra-short electron pulses production. A non-relativistic electron bunch, which is slightly slower than the velocity of light, is injected into the accelerating structure, and then the longitudinal phase space of the bunch is being rotated during acceleration. According to a numerical simulation, ∼ 50 fs bunch can be produced by using the t-ACTS accelerator configuration. Proof-of-principle experiment of velocity bunching has been carried out by observing sub-picosecond electron pulse using a streak camera. We have succeeded in producing a sub-picosecond electron pulse in the t-ACTS. The details of the experiment for ultra-short electron pulse are described in this paper.