Equi-distantly distributed multi-peak frequency spectrum was observed in a high-power 300-GHz band gyrotron for the case of strong reflection off the vacuum window. An oscillation mode different from the design mode can oscillate by adjusting the magnetic field in the cavity. However, a large fraction of the output wave is reflected by the vacuum window. The reflected wave returns to the cavity through an internal mode converter. The azimuthal rotating direction of the reflected wave is opposite to that of the oscillating mode. A theoretical calculation of mode competition between the oscillating co-rotating mode and the counter-rotating mode originating from the reflected wave very well reproduces the observed frequency spectrum. The multi-peak frequency spectrum stems from periodic amplitude oscillation caused by the mode competition between the co-rotating mode and the counter-rotating mode. The frequency interval between the peaks is not simply decided by the round-trip time between the cavity and the vacuum window but determined by the period of the amplitude oscillation.

中文翻译：

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反射对高功率亚太赫兹回旋管中模式竞争和多频振荡的影响：实验观察和理论分析

在高功率300 GHz波段回旋加速器中，在真空窗口强烈反射的情况下，观察到了等距分布的多峰频谱。与设计模式不同的振荡模式可以通过调节空腔中的磁场来振荡。但是，大部分输出波会被真空窗口反射。反射波通过内部模式转换器返回腔。反射波的方位旋转方向与振荡模式相反。从反射波产生的振荡同向旋转模式和反向旋转模式之间的模式竞争的理论计算可以很好地再现观察到的频谱。多峰频谱源于由同向旋转模式和反向旋转模式之间的模式竞争引起的周期性振幅振荡。峰值之间的频率间隔不仅由空腔和真空窗口之间的往返时间决定，还由振幅振荡的周期决定。