| Recently, it was found experimentally that injected plasma into the microwave apparatus enhanced the interaction efficiency and the output power much more than the vacuum cases. Plasma also can improve the transmission quality of electron beam so much as make beam transmission without a guiding magnetic field. All-Russian Electrotechnical Institute(VEI), Moscow, Hughes Research Laboratories and University of Maryland have reported their achievements in this area of research. At present, much research in this area has been carried out in Institute of High Energy Electronics, University of Electronic Science and Technology of China.In this dissertation, the characteristics of the plasma-filled coupled-cavity slow-wave structure under different axial magnet fields are analyzed, and the experimental study of the plasma cathode electron gun is presented.The general method of the circuit model is regarded as unsuitable for the study of the magnetic plasma-filled coupled-cavity slow-wave structure, especially when the density of the plasma exceeds a certain threshold which makes the plasma frequency exceeds the frequencies of the structure modes. We utilize the dyadic Green's functions and the method of matching boundary conditions to establish the dispersion equation of the plasma-filled coupled-cavity slow-wave structure, and then solving the equation by the method of moments.Base on the method of vector eigenfunction expansion, using the mapping in one-dimensional space of the boundary conditions of vector wave functions, we construct the dyadic Green's function and derive the magnetic field vector operators and obtain the admittance-matrix elements of the vacuum parts.The double component particles plasma tensor dielectric permittivity in the arbitrary axial magnetic field are obtained from the Maxwell's equations and the double component plasma particle linear movement equations. By means of the Floquet theorem, we derive the field expressions for the magnetic plasma-filled beam drifting channel, and accordingly, the magnetic field vector operator, the admittance-matrix elements of the plasma region and the flux of energy are obtained.A program for calculating the features of the CCSWS is developed base on the method above. According to the cold test result of certain coupled-cavity traveling wave tube(961HA), we verify the precision of the program. And then, we analyze the characteristics of the coupled-cavity slow-wave structure under the low-density plasma filled conditions. From the analyses, we come to a conclusion that, the low-density plasma-filling cannot modify the field's distribution of the beam drifting channel, and the bandwidth, coupling impedance have not a meaningful enhancement.When the plasma frequency exceeds the frequencies of the cavity-mode, the plasma-cavity hybrid modes appear in the slow-wave structure, and these modes almost fill-up the dispersion space. Throught the numerical calculations we conclude that the dispersion characteristic is determined by the following three aspects, (1) the dememsion of every part of the CCSWS. (2) density of the plasma in the drifting channel which is indicated by the plasma frequency. (3) the amplitude of the external longitudinal magnetic field which is indicated by the gyromagnetic frequency. Due to the generating of the hybrid-modes, and setting proper size of every part of the CCSWS, plasma frequency and gyromagnetic frequency, we can obtain a meaningful enhancement on the bandwidth and the coupling impedance of the CCSWS.The plasma cathode electron gun is a new kind of high-current, long-pulse intense electron beam source which is used in the PASOTRON first. The preliminary design of the plasma cathode e-gun is presented in this dissertation, and experiments has been done in continuous filled-in gases and gases-puff condition, the discharging current and collector current we got show that the plasma cathode e-gun can take the place of material cathode e-gun, especially in plasma filled microwave tubes.
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