高次模回旋管中的非工作模式抑制研究

Study on the Mode Suppression of a High-Order Mode Gyrotron

将高次模回旋管中的竞争模式分为与工作模式角向指标相同的寄生模式和角向指标不同的暂态模式,选择TE32,5为0.4 THz高次模回旋管的工作模式,对不同类型的非工作模式抑制方法展开讨论。结果表明,针对寄生模式,通过优化设计光滑缓变结构的谐振腔来抑制;暂态模式可以通过精心选择工作模式,深入研究注波耦合系数和不同模式的起振电流,合理设置高次模回旋管电子注电压、电流、横纵速度比、引导中心半径等工作参数,使工作模式在某一工作磁场范围内起振电流最低而优先起振,从而抑制暂态模式起振。

High-order mode gyrotron oscillators are promising sources of the high power of millimeter wave and sub-millimeter wave electromagnetic radiation. The characters of the high-order mode gyrotron are affected by the intense mode competition. The competition modes in the gyrotron are divided into the modes with the same number of an azimuthal index and the modes with the different number of an azimuthal index, which are called the parasitic modes and the transient modes respectively in this paper. The methods of the mode suppression are discussed when the TE32,5 mode is regarded as the operating mode of a 0.4 THz high-order mode gyrotron. The parasitic modes can be suppressed efficiently by designing a gradually tapered cavity. Though studying the beam-wave coupling coefficient and the start currents of the relative modes, and then selecting the operating mode carefully, the transient modes can be avoided by putting up properly the parameters of the electron beam： the beam voltage, beam current, pitch factor and beam radius of the guiding center.