A particle-in-cell simulation of a cyclic beam buncher

Cyclic beam bunching has been demonstrated in a numerical simulation of a 35-MeV (γ=69), 4.2-GW relativistic electron beam injected into a cylindrical cavity in which a TE RF mode is circulating. For a 4-MV/m peak field amplitude in the TE₅₁₁ mode and an RF frequency of 1.7 GHz, a modulation index of 6.3 was achieved, with beam bunches appearing every 0.6 ns at the plane of maximum interaction angle, θ=(5/6)2π rad. The simulation results were found to be in close agreement with the linear single-particle theoretical results of F.S. Felber et al. (1983). Also in agreement with Felber et al., the simulations showed that low-emittance bean bunching is possible as long as the RF-field energy dominates the self-field energy of the bunched beam