CHRISTINE 3D: a 3D multi-frequency large signal simulation code for helix traveling wave tubes
A generalization of the theory and implementation of the original CHRISTINE code to three dimensions will be described. The beam is treated as a collection of rays, rather than as disks as in 1D codes like CHRISTINE, and the complete 3D trajectories are followed by the code. This treatment permits the computation of helix intercept current and transverse beam distributions at the entrance to the collector-important design data that are unavailable from a 1D code. The beam may be initialized either by an internal parametric model, including transverse beam current distribution and beam temperature, or by importation of initial data from a gun code. The magnetic focusing field may also be represented by simple parametric models or by actual magnetic field data that is imported from a magnetics code. The RF fields supported by the helix are represented by modal expansion; the full (Bessel function) radial dependence is included. As in the original CHRISTINE, the new code employs models for sheath and tape helices that may be used in parametric studies. Alternatively, the code accepts a table of user-provided data for the circuit dispersion and interaction impedance. Also as in the original 1D code, the new code allows for tapered circuit properties, and for user specified attenuation profiles.