Analysis and suppression of non-rotationally symmetric TE11 mode competition in an X-band relativistic klystron oscillator

In the X-band relativistic klystron oscillator, mode hopping phenomena in the output microwave caused by low-order asymmetric TE11 mode competition are observed. Based on theoretical and simulation analyses of the electron conductance and external quality factors of the main mode TM013 and the TM113 mode, it is found that the electronic conductivity of both the main mode and the low-order TM113 mode is negative, and their external quality factors are close, which is the cause of the asymmetric mode competition. In particle simulations, by altering a pre-reflection cavity and altering the position of the cathode block, the reflection coefficient of the main mode TM013 is increased, thereby enhancing the resonance characteristics of the main mode and effectively suppressing the asymmetric mode competition. Simulation and experimental results indicate that by adjusting the depth of the pre-cavity and reducing the distance of the cathode block, the low-order asymmetric TE11 mode is effectively suppressed, enhancing the stability of the output microwave.