Study of suppressing backward-wave oscillation in a helix traveling wave tube

The influence of uniform magnetic field or PPM(periodic permanent magnetic) field on suppressing BWO(back-wave oscillation) is analyzed on the basis of the 2-D small signal model. It shows that it is possible to increase the start oscillation length by tailoring magnetic field's amplitude and its period without changing the synchronous condition of the fundamental wave; in the meantime, when there are two or more azimuthally asymmetric space harmonics in the high power broad-band helix TWT(traveling wave tube), the influences of the Pierce's gain parameter, space charge parameter, and loss parameter on the start oscillation length and real starting asynchronous velocity parameter are also analyzed. Thus the optimum values of the focusing magnetic field, electron beam and helical slow wave