Large Signal Characteristics Of The Plasma-filled Coupled Cavity Traveling Wave Tube

It has been shown in many researches that by injecting plasma into the vacuum microwave devices, the interaction efficiency can be increased greatly, so that the output power can also be enhanced at the same input condition.The beam-wave interaction characteristics of the hybrid wave in the coupled-cavity TWT of plasma-cavity hybrid mode is studied in the dissertation.1. How the hybrid wave between the cavity mode and plasma mode is formed is studied. The results show the expansion of the "cold " bandwidth and the "warm" bandwidth. When the density of plasma increase to a certain scale, in this case, the cavity mode of the CC chain overlaps the TG mode, these two modes coupled each other and form the so called hybrid modes. The hybrid modes cover a larger bandwidth than that of the vacuum case, so the "cold " bandwidth is expanded very significantly. By adjusting the beam parameters, the space charge line will intersect with the hybrid mode, the intersection region are enlarged instead of a point, so the beam and the wave can maintain the phase in step in a large range, thus the "warm" bandwidth is expanded too. It should be noted that when operating at the hybrid modes, the coupled impedance is increased 5 times approximately larger than that of the vacuum case. Totally speaking, the slow wave characteristics are improved substantially due to the formation of the hybrid wave.2. The self-consistent working equations of nonlinear beam-wave interaction have been obtained. The equations include the circuitry equation considering reverse radiate and moving-electron equation considering relativity, and the complex amplitude equation of n harmonics in high frequency electron current. The self-consistent working equations are the basic equations that are used for studying nonlinear beam-wave interaction characteristics.3. By using variable-separated theory, the potential energy equation in space charge field was derived. The plasma satisfied the common static potential energy equation since the anisotropy of the plasma. The solving method of the common static potential energy equations is indicated in the paper. The space charge field has the essence distinction in the vacuum and the electric channel with plasma-background. The space charge field in the vacuum is decreased under the exponential trend, but the space charge field in the plasma is oscillation form andpropagating faraway. That is explain of the space charge field has different effect to beam-wave interaction in the plasma- background and vacuum-background.4. Using method of four-rank Runge-kutta, the big signal characteristic analysis code was compiled by VC++. It is shown that more than 40 percent of the efficiency will be achieved that more than CCTWT in vacuum-background. At the same time, the change of efficiency, power and gain when considering space charge field or not is also be analyzed, we find when space charge field is taken into account, the efficiency can be increased and the saturation length can be shortened. Nevertheless when space charge field is taken into account, the saturation length lengthened and the efficiency decreased in the vacuum-background. The contrary phenomena mean an essential distinction. Finally, the big signal characteristic of beam-wave interactive was analyzed when input power and density of plasma-background was different, the analysis result indicates that input power have little effect on output power. The efficiency will increase when the density of plasma increased. But when the density increased to a certain value, the efficiency will decrease when the density of the plasma increased. The reason is the range of overlap frequency between hybrid mode G1 and G2 will increase when density of plasma-background increases. Under the condition of the same input frequency, the best beam-wave synchronization condition is not satisfied, so the efficiency will decrease in contrast.