High Frequency Characteristic And Mode Purification Research Of Overmoded O-type Cerenkov Oscillators

In recent years, overmoded devices have been developed extensively for its superiority over single-mode devices in power, pulse width and efficiency, overmoded O-type Cerenkov oscillators are typical representatives. Theoretical and emulational research are conducted towards high frequency structure characteristic, hot-cavity mode component analysis and purification of the output mode in this paper, aiming at settling solid foundation for the following research. The main content is as follows:Firstly, mode matching method is employed in order to get S parameter which describes the resonance characteristics of the whole tube quickly and precisely. Elaborate and grasp the idea and the deducing method of mode matching method, then deduce the mode matching formulas of circular waveguide in detail, write program to solve and analyze some examples. The result is well matching which is simulated by HFSS, which shows that we can use mode matching method to get the S parameter of a complex structure quickly.Secondly, in order to analyze the mode component consisting electron beam such as collimator, dispersion equation of circular waveguide considering electron beam is deduced, and solve the equation numerically, then contrast the result with the situation that no electron beam is considered, the result shows that the dispersion curve is lifted by the electron beam. The influence of thickness of the e-beam, plasma frequency and location of the e-beam to the dispersion curve are discussed respectively, the result shows that location of the e-beam influence the dispersion curve comparatively large, while the plasma frequency and location of the e-beam influence the dispersion curve comparatively small. Method to get the component of output mode is introduced, taking the influence of e-beam to the dispersion curve into account, and analyze the hot cavity mode component in collimation hole and drift section of an X band overmoded Cerenkov oscillator respectively, it shows that the mode component in collimation hole is accurate, while the mode component in drift section is not that accurate.Lastly, in order to purify the output mode of overmoded devices, and use mode coupling method during calculation, mode coupling method is introduced, and the mode coupling equation of gradually radius changing waveguide is presented, write program to solve an example numerically, and the result is well matching the result in the document. The thought and method of purification to the output mode is elaborated, and using the mode coupling method into the design and calculation of solving the mode purification device, mainly to determine the initial phase relation to purify two modes, which can guide the design of phase adjust straight waveguide. Design a mode purification device of a X band overmoded RBWO using this method, and hot-cavity simulation of the whole tube is conducted, the result is pretty good. At last, a discussion is made towards the possible problems of the mode purification devices in application.