In the development of a Ka-band overmoded Cerenkov oscillator, the issue of asymmetric modes competition should be paid attention to as they can be potentially excited in the overmoded cavity and then affect the performance of device seriously. Based on the 3-D models, the influences of the structural parameter such as “ldr” on the resonance characteristics for the symmetric modes and the asymmetric modes are analyzed. Then according to the start conditions for the modes, the roles of the Ezfield distribution and the guiding magnetic field in spurring the asymmetric modes are discussed and accordingly the ways to alleviate the asymmetric modes competition are suggested. The 3-D particle-in-cell (PIC) simulation results show that, with the proposed conditions, the optimized device is operating stably with a purified output mode of TM 01 . Finally, the optimized structure is experimentally tested. In accordance with the theoretical prediction and the simulation results, the experimental results show that under specific conditions the asymmetric modes are very likely to be excited and they can even dominate the beam-wave interaction process. Nevertheless, using the proposed method, the output mode is pure of TM 01 , demonstrating the feasibility of the proposed method in suppressing the asymmetric modes competition.

中文翻译：

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超模Ka波段切伦科夫振荡器中不对称模式竞争的理论与实验研究


在Ka波段过调制切伦科夫振荡器的开发中，应注意非对称模竞争问题，因为它们可能在过调制腔中被激发，从而严重影响器件的性能。基于3D模型，分析了“ldr”等结构参数对对称模式和非对称模式谐振特性的影响。然后根据模式的启动条件，讨论了Ezfield分布和引导磁场在激励非对称模式中的作用，并据此提出了缓解非对称模式竞争的方法。 3-D颗粒细胞（PIC）仿真结果表明，在所提出的条件下，优化后的器件能够以TM 01 的纯化输出模式稳定运行。最后对优化后的结构进行了实验测试。根据理论预测和模拟结果，实验结果表明，在特定条件下，非对称模态很可能被激发，甚至可以主导束波相互作用过程。然而，使用所提出的方法，输出模式是纯TM 01 ，证明了所提出的方法在抑制非对称模式竞争方面的可行性。