Theoretical research on the performance of a practical helix travelling wave tube

On the basis of a rigorous field theory, two different physicalmodels of attenuator and sever have been proposed. One is named Highattenuation (HATT) model in which both attenuator and sever areconsidered as a unified attenuator, but the sever is regarded as anarea of very high loss; the other is called Sever and attenuator(SATT) model in which the sever is modelled as a drift area in whichthe electric and magnetic fields both vanish. A complex function isderived and potential sinking effect is also considered. Thus, a setof more practical self-consistent equations of nonlinear beam--waveinteraction is formulated. Simulations are carried out under theconditions of the two different physical models, and the simulationresults are compared with the experimental data. The results showthat in the case of single signal drive, the unknown second harmonicshould be included for predicting the saturated output power. It isalso evident that the SATT model and the HATT model predict the samephysical nature, whereas the results predicted by the HATT model aremuch closer to the experimental data than those obtained from theSATT model. Therefore, these results provide a strong theoreticalbasis for designing broadband and high gain helix travelling wavetubes.