Self-consistent and complete field theory of relativistic travelling wave tube amplifier with plasma loaded tape helix

Abstract

The dispersion relation was derived for electromagnetic wave propagation through a plasma-loaded helix travelling wave tube (TWT). The analysis is based on field theory for a configuration in which a magnetized pencil-type beam propagates through cold plasma in the helix enclosed with a loss-free wall. The obtained dispersion relation implicitly includes azimuthal variations and all spatial harmonics of the tape helix. The characteristics of the growth rate were studied numerically. The results show that the phase velocity increases with increasing plasma density and axial magnetic field. By numerical computation, the dispersion characteristic of plasma-loaded helix TWT analyzed in different cases of various plasma densities, beam energy, beam density, and axial guide magnetic field. The results show that the presence of plasma significantly increases the growth rate and bandwidth. The enhancement in beam energy and density cause an increase in growth rate and frequency. The growth rate increases with increasing axial field until is reaches a maximum; further increases in the axial guide field lead to a relatively constant growth rate.