| Traveling wave Tubes (TWT) are high gain, broadband, high efficiency, and high power microwave amplifiers, which are widely used in modern military electronic equipments, such as communications, radars, electronic warfare, etc. 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 disk-loaded TWT of plasma-cavity hybrid mode is studied in the dissertation.1. Although the symmetry TM01 mode is the main mode, research about the asymmetry mode of disk-loaded waveguide is necessary. Considering the asymmetry mode, the general dispersion equations and interaction impedance expressions of disk-loaded waveguide are obtained through strict field theory.2. Based on the Maxwell equations, the basic equation of the slow-wave structure filled with plasma in the finite magnetic field is deduced. The dispersion equation and interaction impedance of the disk-loaded waveguide filled with magneticed plasma are studied in the strong longitudinal magnetic field for the first time, which proves that the frequency of the TM01 mode upshifts and interaction impedance increases as the density of the plasma increases. When a periodic structure is loaded with plasma, the spectrum of the TG modes (Trivelpiece-Gould modes) will become abundant. As the plasma density increases to a large scale, it also can be found that the TM01 mode of the disk-loaded waveguide overlaps the TG mode. These two modes couple with each other and form the new hybrid modes G1, G2.3. The uniform self-consistent working equations of nonlinear beam-wave interaction between slow electromagnetic traveling wave and electron beam have been obtained, using the theory of mode functions and orthogonality. The equations include excited equation, motion equation, energy conversion equation, phase evolving equation, etc. which can simulate the beam-wave interaction process in relativistic TWT and multi-signal multi-mode TWT.4. By using variable-separated theory, the potential energy equation in space charge filed 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 filed 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 and propagating faraway. That is explain of the space charge filed has different effect to beam-wave interaction in the plasma-background and vacuum-background.5. 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 increase. |
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