LINEARIZED FIELD-THEORY OF A DIELECTRIC-LOADED HELIX TRAVELING-WAVE TUBE AMPLIFIER

A linearized relativistic field theory of a helix traveling wave tube (TWT) is presented for a configuration where either a thin annular bea m or a solid beam propagates through a sheath helix enclosed within a loss-free wall in which the gap between the helix and the outer wall i s filled with a dielectric, A linear analysis of the interaction is so lved subject to the boundary conditions imposed by the beam, helix, an d wail, In the case of the annular beam, the electrons are assumed to be strongly magnetized. In contrast, the effect of variations in the a xial magnetic held are included in the electron dynamics for the solid beam analysis, Determinantal dispersion equations are obtained for th e azimuthally symmetric modes which implicitly includes beam space-cha rge effects without recourse to a heuristic model of the space-charge field. Numerical solutions of the dispersion equations are discussed a nd compared with experiments.