Simulation of Drive-Induced Oscillations in Helix Traveling-Wave Tubes

Drive-induced oscillations (DIOs) in helix traveling-wave tubes (TWTs) may occur during large-signal amplifier operation. As the kinetic beam energy is reduced, the beam-wave synchronism possibly shifts into the π-point, thus enabling simultaneous interaction with the forward and the backward circuit mode. There, asymmetries in the beam-wave interaction region introduce an additional coupling mechanism and lower the oscillation threshold compared with backward-wave oscillations (BWOs). Consequently, DIOs are likely to arise. In addition even without asymmetries, drive-induced BWOs are observed. A hybrid timeand frequency-domain simulation approach is presented and applied to analyze this phenomenon in a helix TWT. In addition, an effective suppression technique is proposed.