.220 Ghz Higher Order Mode Gyrotron Research

Gyrotron is based on instability of electrons cyclotron resonance, is developed for amplifier and oscillator at millimeter and sub-millimeter wave band. Gyrotron oscillator is the most significant and most mature gyrotron. Considering application, there are two kinds of gyrotron oscillator: One is used for electron cyclotron heating of plasma fusion, it demand that output power of the gyrotron can be as large as 1 MW. For this reason, high order cavity mode and Whispering Gallery mode which possesses high mode stability are adopted commonly; the other is moderate power (25~50kw) gyrotron operating at the ISM (industrial, scientific, medical) frequency. For this reason, low wastage rotationally symmetric mode or low order mode is used.Gyrotron design in theory has many methods for choice, such as fundamental or high harmonic, low or high order mode, single or complex cavity interaction circuit. Different method has different technique character. Low-order fundamental-harmonic gyrotron possess many advantages such as simple cavity structure, low technique difficulty and steady state. However, with the increase of operating frequency, cavity transverse size decreased rapidly, which cause power capability fall. Thereby high order mode is adopted to increase cavity size and output powery. However, it also brings mode competition. The thesis is just focused on the above problems. Main research object is a gyrotron which operating in high-order mode at 220GHz. Based on research of work mechanism and beam-wave interaction. The main results are as follows:1. According to linear theory of gyrotron, profile distribution function and start current in resonance cavity have been carried out. It can be confirmed operating mode and suppressed competition mode by adopting linear mode selection theory.2. Based on Non self-consistent and self-consistent of nonlinear theory of gyrotron, compile self consistent and non-self consistent interaction simulation software in high-order mode weakly-irregular cavity gyrotron. Plenty of simulation and investigation for the weakly irregular gyrotron at 220GHz have been carried out.3. The effect of cavity geometry parameter, electron guiding centre radii, beam velocity spread, electron-beam misalignment and speed ratio on beam-wave interaction and mode competition have been accomplished. At the same time, to assure single mode work, nonlinear theory is used to mode selection.