Title: Beam tuning and bunch length measurement in the bunch compression operation at the cERL,
Abstract: Realization of a short bunch beam by manipulating the longitudinal phase
space distribution with a finite longitudinal dispersion following an off-crest
accelera- tion is a widely used technique. The technique was applied in a
compact test accelerator of an energy-recovery linac scheme for compressing the
bunch length at the return loop. A diagnostic system utilizing coherent
transition radiation was developed for the beam tuning and for estimating the
bunch length. By scanning the beam parameters, we experimentally found the best
condition for the bunch compression. The RMS bunch length of 250+-50 fs was
obtained at a bunch charge of 2 pC. This result confirmed the design and the
tuning pro- cedure of the bunch compression operation for the future
energy-recovery linac (ERL).