Analysis of backward wave oscillations for a stable TWT amplifier

Two wave theory (considering the forward slow wave and forward fast wave) has been used to calculate the velocity taper as a remedy for the higher pass band backward wave oscillations in a TWT. Such oscillations in fact are the main factor which limits the practical beam current in high-power TWTs. Based upon the two wave theory, a model has been developed to study the effect of various tube parameters on the backward wave oscillations. Using this model, the effect of following parameters have been studied on the backward wave oscillation conditions in the TWT: (a) Helix Length (b) Tapering Parameter (c) Frequency Parameter (d) Growth constant etc. A software program has been developed on the basis of model and the stability conditions of a Ku-band, 140 watt space TWT has been analyzed under the following conditions of helix slow wave structure. (1) Untapered Slow wave structure, (2) Tapered slow wave structure having two parts of equal length (3)Tapered slow wave structure with parts of unequal length.