Investigation of the mechanisms of pulse amplification in helical traveling wave tubes

The helix Traveling Wave Tube (TWT) is a vacuum electronic device which utilizes an electron beam to amplify an electromagnetic wave. Until recently, the helix TWT, although having a broad frequency gain bandwidth compared to other vacuum electron devices, was used in relatively narrowband ways in its applications in communications and electronic countermeasures. Recent interest in ultra-wideband radio and radar, combined with recent development of ultra-wideband helix TWTs, has stimulated interest in the amplification of very broadband multi-frequency signals and impulses. A number of studies have been done on the harmonic and inter-modulation effects of multiple signals in a helix TWT, but there has not been much investigation into impulse amplification. This study investigates the impulse response of a helix TWT. It presents a new non-linear 1D time domain model of a helix TWT, shows the possibility of modeling the impulse response in the frequency domain, and favorably compares the models' predictions to the experimental measurements of impulse response on a wideband research TWT. It then explains observed differences in the TWTs response to positive and negative input impulses and discusses the growth and saturation mechanisms for a positive gaussian impulse input.