Some transient phenomena in microwave tubes

The paper describes investigations into the effects of pulsing the beam in a microwave tube. Although a sharp beam front suffers very little distortion on travelling down a helix or a drift tube, experiments indicated that a beam front does impress a large video signal on the circuit of a travelling-wave tube which, owing to reflections at the ends of the circuit, i.e. the helix, causes the circuit voltage to ring. The build-up of r.f. signals during this ringing period is studied. The build-up process in a backward-wave oscillator has been analysed, and expressions for the rate of build-up as a function of beam current have been derived for the zero-space-charge and large-space-charge cases. These expressions were compared with experimental results obtained from a helix-type S-band tube. A similar analysis has been carried out for the case of build-up in a 2-cavity feedback klystron oscillator.