A complete space-charge model for 3D structures in the CHRISTINE 3D large-signal code

The CHRISTINE 3D code was developed to simulate the large-signal characteristics of slow-wave devices using a fast, parametric model. The model includes a fully three-dimensional representation of both particle motion and electromagnetic fields, treating external fields, the traveling-wave circuit field, and the RF space-charge field separately, but self-consistently. In common with existing parametric large-signal models, the space-charge fields (due to the beam charges) are computed assuming that they exist only within a cylindrical pipe at the inner radius of the circuit structures. In this paper, we develop a method for correcting the space-charge field to take account of the true 3D geometry. The correction terms are pre-computed using the 3D electromagnetic simulation code CTLSS, and the additional fields are included in the non-linear simulation. The corrected model shows a reduction in predicted gain.