Beam Dynamics for a High Field C-Band Hybrid Photoinjector

In this paper, we present a new class of a hybrid photoinjector in C-Band. This project is the effort result of a UCLA/Sapienza/INFN-LNF/RadiaBeam collaboration. This device is an integrated structure consisting of an initial standing-wave 2.5-cell gun connected to a traveling-wave section at the input coupler. Such a scheme nearly avoids power reflection back to the klystron, removing the need for a high-power circulator. It also introduces strong velocity bunching due to a 90° phase shift in the accelerating field. A relatively high cathode electric field of 120 MV/m produces a 4 MeV beam with ∼ 20 MW input RF power in a small foot-print. The beam transverse dynamics are controlled with a ∼ 0.27 T focusing solenoid. We show the simulation results of the RF/magnetic design and the optimized beam dynamics that shows 6D phase space compensation at 250 pC. Proper beam shaping at the cathode yields a 0.5 mm-mrad transverse emittance. A beam waist occurs simultaneously with a longitudinal focus of < 400 fs rms and peak current >600 A. We discuss application of this injector to an Inverse-Compton Scattering system and present corresponding start-to-end beam dynamics simulations.