Dynamic defocusing of electron beams in high-power helical traveling-wave tubes with length-dependent dispersion

Dynamic defocusing in a wideband helical traveling-wave tube (TWT) with an output power of 1.5–2.0 kW in the continuous-operation mode is analyzed. The TWT contains fragments with normal and anomalous dispersion of the phase velocity. It is demonstrated that the TWT output characteristics can be improved and the TWT stability against self-excitation on the backward wave can be increased with the use of appropriate values of parameters of the electron-optical system that forms a converging axially symmetric beam focused by a periodic permanent-magnet focusing system.