Preliminary computational study on minimizing longitudinal emittance in photoinjector

Recently, we proposed a novel photoinjector that incorporates an emittance exchange (EEX) beamline. Previous studies demonstrated promising 4D emittance performance of an EEX-based injector, but the beam’s longitudinal emittance at the linac exit still limits the final transverse emittance downstream of the EEX stage. We performed a comprehensive scan of injector parameters—including gun phase, laser spot size and pulse length, and solenoid strengths—to (1) estimate the minimum achievable longitudinal emittance, (2) identify sources of emittance growth, and (3) explore mitigation strategies. Here, we present the status of this study. Simulations were carried out using General Particle Tracer (GPT) including space-charge effects.