Backward-wave oscillation suppression in helix traveling-wave tubes by magnetic field tapering

Two techniques for suppressing backward-wave oscillations in homogeneous helix sections of traveling-wave tubes are presented. For this purpose, the focusing magnetic field is modified. The first technique aims at compressing the electron beam in order to reduce beam-wave coupling. The second one changes the beam rotation to affect the backward-wave interaction. Both techniques increase the margin against backward-wave oscillations significantly. Theory and simulation results are presented and compared.