Simulations of beam–beam interaction in an energy recovery linac

Interactions between accelerated beams and reinjected spent beams in an energy recovery linac (ERL) were studied numerically aiming at an enhanced efficiency and a reduced shielding load. With low injector energy, 1 MeV, the orthodox scheme for reinjecting spent beams, on one hand, is found to result in undesirable beam-loading deviations in an ERL owing to velocity variations of the beams. On the other hand, a counter reinjection scheme is found to be effective for suppressing the deviations, but it is also found to result in an appreciable degradation in a fresh beamʹs properties due to enhanced beam–beam interactions. To realize the advantages of both of these two schemes, a new combined scheme for an ERL-based FEL is proposed. Also the effects of spent beams’ properties on fresh beams’ emittances are discussed.