Pierce-Type One-Dimensional Eulerian Hydrodynamic Analysis of a Plasma-Filled Helix Traveling-Wave Tube

Forward- and backward-wave interaction analyses of a plasma-filled helix traveling-wave tube are developed following the Eulerian hydrodynamic approach and taking into account the effects of the following three factors: 1) the thermal velocity of plasma electrons; 2) collisions between the plasma electrons; and 3) the finite diameter of the electron beam and its proximity to a metallic boundary. The electron beam is treated as a moving charged fluid, and the plasma is treated as a stationary quasineutral fluid. The coupled circuit and the electronic equations are developed, and a Pierce-type hot (beam-present) dispersion relation is obtained, which is then interpreted for the forward-wave gain-frequency response and for the backward-wave oscillation criterion of the device. In the absence of the slow-wave structure, the dispersion relation reduces to that of a beam-plasma amplifier, whereas in the absence of the plasma, the dispersion relation passes on to that of a conventional vacuum traveling-wave tube. The analysis is further validated with an existing forward-wave interaction analysis of a plasma-assisted helix traveling-wave tube that treats the beam-wave interaction in the device as a boundary-value problem by considering the beam-plasma system as a propagating medium of an equivalent relative permittivity tensor. Interestingly, similar to a beam-plasma amplifier, a plasma-filled TWT supports no backward-wave oscillation in the reactive-plasma convective instability.