| The trends of compactness and high gradient for higher energy particle accelerators push forward the development of microwave tubes, such as the high power, high frequency and high efficiency klystrons. Axisymmetric microwave sources suffer from fundamental power output limitations which result from the conflicting requirements of small beam sizes and high beam current. The sheet beam klystron(SBK) is a new kind of microwave vacuum device with higher beam-wave interaction efficiency, which can decrease the space charge effects by increasing space charge limited current. The SBK was studied theoretically and numerically in this dissertation.The high frequency structure of barbell-shaped cavity and three-gap extended interaction cavity in Ka-band SBK were studied first. The frequency characteristics and field distribution of the operating mode in the resonator were calculated. The relation between the operating frequencies and the structure parameters was obtained. The π-mode and 2π-mode of three-gap extended interaction cavity was compared.Secondly, the relationships that the energy exchange between electron beam and the operating mode varies with the transit angle, which were analyzed by using of one-dimensional small signal theory and the basic dynamic theory. The formulation of load conductance of electrons and efficiency of the 2π-mode in the resonator were given.The high frequency characteristics of the Ka-band SBK was studied by FDTD algorithm. The influence of the coupling hole on the cavity frequency, field distribution and the Qext value were studied. Meanwhile, different feed methods were compared. It was obtained that the two side feed method was better than single side feed method. Then the tuning for idlers and the quasi-optical output coupler for output cavity were considered.The Ka-band SBK was investigated numerically by 3-D PIC codes. Simulation results show that for a 500 k V, 1k A, 28:1 aspect ratio sheet beam with 0.8T guiding magnetic field and 40.060 GHz, 7.6W seed power, the SBK was capable of generating an output power higher than 186 MW with gain of 73.9d B. The power conversion efficiency is 37.2% and the-3d B bandwidth is 150 MHz. |
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