Nonlinear eulerian hydrodynamical analysis of helix traveling-wave tubes for harmonic generation and its control

Eulerian hydrodynamics was developed to study the nonlinear problem of seco nd harmonic generation in a helix traveling-wave tube (TWT), A closed-form expression for the second-harmonic component of RF output power was obtaine d, The method required the specification of the dispersion and interaction impedance characteristics of the helical slow-wave structure (SWS) used in the device, obtainable by the field analysis of the SWS. Care was taken how ever to restrict the present Eulerian theory to the correct regime, which w as found in terms of the RF input power drive and the device interaction le ngth, by validating the theory against the more accurate Lagrangian theory, Within this regime, that was below the saturation level of the device, the effect of the dispersion of the SWS on the second harmonic generated in th e device was studied. It was found that, irrespective of whether the dispersion of the SWS is pos itive or negative, the second harmonic content of the device decreased with the amount of the dispersion. Furthermore, though both the fundamental and the second harmonic content of the device decreased with the distributed l oss on the SWS, the second harmonic relative to the fundamental showed a mi nimum at an optimum value of the distributed loss.