Research On Physical Problems In A Helix Traveling Wave Tube

Traveling Wave Tube (TWT) is one of the most important types of the microwave/millimeter wave vacuum tubes. Due to its high power, high gain, high efficiency and broadband, it is widely used in modern military electronic equipments, such as communications, radars, electron warfare, etc. In this dissertation, we made theoretical study on three important aspects in detail, i.e., RF characteristics of helix Slow Wave Structure (SWS), the suppression of Backward Wave Oscillation (BWO) and self-consistent nonlinear beam-wave interaction. Several important and valuable results are achieved and listed as follows:1. The tape helix model was set up by considering the helical thickness, the helical width and the surface current on the helix, arbitrary number and arbitrary shape rods, loaded vanes and metal envelop. This model is suitable for analyzing the narrow and wide tape helix. Then we carried out rigorous theoretical analysis through field theory and achieved dispersion equation, interaction impedance, and attenuation constant.2. In order to enhance the power capability of the helix traveling wave tube, a novel tape helix SWS, which is supported by helically arrayed radial dielectric-support posts, was put forward. Each dielectric post can be easily brazed with the tape helix and the metal envelope by means of a special soldering. This kind of supporting mode can protect the dielectric-support posts from being broken by the thermal stress in the case of high temperature. A hybrid model was set up in consideration of the influences of both the radial thickness of the tape helix and these discrete dielectric-support posts. The calculated results using this hybrid model show good agreements with the HFSS simulation results.3. One of the most important measures that are used to make TWT work stably and reliably is to suppress all kinds of self-oscillations, including BWO. On the basis of the coupled mode theory, considering the effects of attenuator/sever, taper/step phase velocity, voltage gradient of electron beam, etc. on the backward wave start condition, we set up a set of self-consistent linear working equations, including circuit equation, motion equation, and the current continuity equation, and gave corresponding boundary conditions. Numerical calculations show that when the non-uniformities becoming strong, the start oscillation length increases, however, as the phase velocity or beam potential exceeds a particular value, no oscillation condition could be found, and that the start oscillation length decreases when the start position of the attenuator is close to the input section of the SWS, and the relative start oscillation current decreases when the attenuation length increases or the attenuation quantity decreases. Therefore, the effect of the attenuator on the BWO start oscillation condition is actually noticeable.4. Focusing magnetic field tapering is a better method among all kinds of methods used to suppress BWO in a practical TWT, because it hardly change the forward...