GENERATION AND DIAGNOSIS OF ULTRASHORT ELECTRON BUNCHES FROM A PHOTOCATHODE RF GUN LINAC

Ultrashort electron bunches are essential for time-resolved measurement methods such as pulse radiolysis* from the viewpoint of time resolutions. On the other hand, generation of electro-magnetic wave in the THz range using short electron bunches has been investigated**. Frequency spectra of coherent transition radiation (CTR) emitted by an electron bunch depend on bunch form factor (BFF), which is expressed by Fourier coefficients of longitudinal distribution in the electron bunch. In this study, the bunch length measurement was demonstrated by analyzing THz-waves generated by CTR. Femtosecond electron bunches were generated by a laser photocathode RF gun linac and magnetic bunch compressor. THz-waves generated by CTR, which was emitted on an interface of an aluminum mirror along the beam trajectory, were transported to a Michelson interferometer. The bunch length was measured by analyzing interferogram, which was an infrared detector output as a function of a moving mirror position. Finally, the bunch length was measured according to fitting curves for the interferogram near the centerburst***. Minimum bunch length of 1.3 fs was obtained at a bunch charge of ~1 pC.
Proceedings of the 5th Int. Particle Accelerator Conf., IPAC2014, Dresden, Germany