Numerical analysis of velocity bunching for an ERL light source

We investigate feasibility of velocity bunching in the main linac of an energy recovery linac (ERL) by a computational simulation. The simulation performed for eight TESLA-type cavities reveals successful bunch compression from 3.2 ps to 170 fs, which is in good agreement with the analytical prediction. Since the residual energy spread after velocity bunching is considerably smaller than the correlated energy spread required for magnetic compression through recirculation, velocity bunching is useful to realize short-pulse and high-brightness X-rays by ERL. The beam current limitation on velocity bunching is also discussed.