Three-dimensional stability analysis of a helix TWT using CHRISTINE 3D

In this paper we report results from the CHRISTINE 3D code, which we have applied to study the phenomenon of BWO power holes in helix TWT´s. It is widely believed that these power holes, which occur under large signal condition, are due to the amplification of a backward wave space harmonic of a signal at a harmonic of the drive signal wave gain occurs, as illustrated. We show the small signal BWO gain as a function of frequency, for various values of beam radius, as computed by TWT simulation. When the BWO gain is very large, as for the cases 0.065 cm and 0.070 cm, the algorithm used to solve for the wave amplitudes sometimes does not converge; points corresponding to such cases have been omitted.