Microwave breakdown has always been a huge challenge to the development of high-power microwave (HPM) sources. Some unique breakdown phenomena in a novel and powerful overmoded relativistic backward wave oscillator (RBWO) operating at low magnetic field are demonstrated. Three different breakdown mechanisms are utilized to explain these phenomena through detailed electromagnetic field calculation and particle-in-cell demonstration and effective methods are applied or suggested to mitigate the breakdown. The breakdown in the slow wave structure (SWS) mainly results from bombardment by the main electron beam under the intense radial electric field. Increasing the span between the main electron beam and the SWS or applying a coaxial extraction structure operating at coaxial TM₀₁ mode might decrease the radial electric field and lessen the bombardment. The breakdown in the internal reflector originates with the field-induced emission in the inner ring under the intense axial electric field of the TM₀₁ and TM₀₂ mode and the subsequent electron-triggered emission in the outer ring. Removing the central part or constructing a complex reflector surface can suppress the emission. The breakdown in the slot retained for the Rogowski coil results from low pressure gas discharge initiated by microwave leakage from the RBWO into the diode region. Pasting microwave absorbing material into the coaxial diode region helps to obtain normal beam current waveforms measured by the Rogowski coil.

微波击穿一直是高功率微波（HPM）源发展面临的巨大挑战。演示了在低磁场下运行的新颖且强大的过调制相对论后向波振荡器 (RBWO) 中的一些独特击穿现象。通过详细的电磁场计算和细胞内粒子演示，使用三种不同的击穿机制来解释这些现象，并应用或建议有效的方法来减轻击穿。慢波结构（SWS）的击穿主要是由于强径向电场下主电子束的轰击造成的。增加主电子束和 SWS 之间的跨距或应用在同轴 TM _{01 下}运行的同轴提取结构模式可能会降低径向电场并减少轰击。内部反射器的击穿源于在 TM ₀₁和 TM ₀₂模式的强轴向电场下内环中的场致发射以及随后外环中的电子触发发射。去除中心部分或构建复杂的反射器表面可以抑制发射。为 Rogowski 线圈保留的槽中的击穿是由微波从 RBWO 泄漏到二极管区域引发的低压气体放电造成的。将微波吸收材料粘贴到同轴二极管区域有助于获得由 Rogowski 线圈测量的正常束流波形。