Genesis: a 2.5D nonlinear simulation code for helix traveling wave tubes in the frequency domain

Abstract

Summary form only given. A nonlinear analysis of the helix traveling wave tube (TWT) in the frequency domain is presented for a configuration where an electron beam propagates through a sheath helix surrounded by a conducting wall. Dielectric- and vane-loading of the helix are included as is circuit tapering and external focusing by means of either a solenoidal magnetic field or a periodic field produced by a periodic permanent magnet (PPM) stack. These field models permit the treatment of tapered solenoidal and PPM fields. The electromagnetic field is treated as a superposition of waves in the sheath helix approximation in which the amplitudes and phases are assumed to vary slowly in z. The dynamical equations for the field are solved in conjunction with the three-dimensional Lorentz force equations for an ensemble of electrons. Collective effects from the fluctuating RF beam space-charge waves are included by means of a superposition of solutions of the Helmholtz equation. The DC self-fields due to the bulk charge and current densities of the beam are also included. The simulation is compared with a linear theory of the interaction as well as a time-domain simulation model, each of which is applied to an example corresponding to a tube built at Northrop-Grumman Corp.