Mode competition is a severe issue when the gyrotron operates in high order mode or in highharmonic relatively lower order mode.For optimum performance,the gyrotron should operate in one desired mode with an appropriate start-up scenario.This research investigates a 120 GHz gyrotrondesigned for Electron Cyclotron Resonance Heating in plasma fusion tokomak systems,which operates in TE22,6+mode.Time evolution of beam parameters during startup is computed for several types of startup methods and then is used to investigate the oscillating modes.The cavity can oscillate in a single operating mode if an appropriate start-up scenario is chosen.This paper only presents an analysis based on linear theory.Though the theoretical investigationis appliedin fundamental mode in research,it can also be used in highharmonic modes.The result indicates that the triode-type scenario and the other two scenarios are beneficial to the operating mode TE22,6+.%当回旋管工作在高次模式或者高次谐波时,模式竞争尤为剧烈.通常最佳工作状态下,回旋管工作在单模,起振方案对回旋管是否单模工作影响很大.文章研究了等离子体聚变托克马克系统中的应用于电子回旋共振加热的120 GHz回旋管,该回旋管工作模式为TE22,6+,计算了不同起振方案中电子参数的时间演变并将其用于研究模式起振.根据计算结果可知,当设计合适的起振方案后回旋管可工作在单模下.文章基于的理论为线性理论,并且应用的模式为基模,但是该分析方法同样适用于高次谐波.仿真结果显示,三极管类型起振方案和其他两个起振方案下,工作模式TE22,6+可以单独起振.
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