可调电子束注入器调配调谐结构的设计及分析

驻波谐振腔是基于直线加速器的束流注入器的基本构造元件，其大功率微波馈入一般选用矩形波导耦合器，但它会引起场不对称和谐振频率的漂移，也难以针对不同流强的束流灵活调节耦合度。建立了带有调配杆的耦合器的等效电路模型，在理论分析的基础上，给出了杆的最佳位置。此外，在耦合器的对称方向插入调谐杆用于补偿结构改变及加工安装等外部因素造成的频率漂移，并使用 CST MICROWAVE STUDIO 的三维电磁仿真给出了两个杆的尺寸和调整范围。联合调整的仿真结果表明，在谐振频率保持稳定的情况下，不同流强的束流均达到临界耦合状态，从而避免了耦合器失配引起的反射功率风险，并减少了由于较小耦合孔引起的场不对称。

Design and analysis of a tunable coupler for application to adjustable beam injectors

As a fundamental component of a linac-based beam injector, the rectangular-waveguide coupler is a conventional device for feeding high power, but it will induce field asymmetry and resonant-frequency shifting. Furthermore, it is also difficult to adjust the coupling factor for adjustable beam injectors. In this paper, an equivalent circuit model is established for the coupler with a tuning rod. Based on theoretical analysis, the optimal position for the rod is given. Besides, the frequency shifting is corrected by using another rod inserted to the cavity in the opposite direction. Sizes and adjustment ranges of both rods are given by three-dimensional electromagnetic simulation using CST MICROWAVE STUDIO. Jointly adjusted simulation results show that, critical-coupled states are achieved for different beam intensity while the resonant frequency remains stable, thus the risk of reflected power caused by coupler mismatching can be avoided, and the field asymmetry due to a small coupling hole can be reduced.