实现输出模式控制和纯化是过模相对论返波管振荡器物理设计的关键.结合数值仿真和粒子模拟,对一种宽间隙反射器过模相对论返波管内的同频高阶模式激励及其抑制进行了研究,结果表明:模式转换和激励是同频高阶模式的直接来源,合理优化慢波结构、反射器和二极管参数,抑制由工作模式向高阶模式的转化效率,调整由二极管区反射回束波互作用区的模式相位,实现了过模相对论返波管的高效率工作和高模式纯度微波输出;所设计的宽间隙反射器过模相对论返波管输出微波功率中TM01模式的比例高于98%,功率转换效率约40%,工作频率为9.87 GHz.

The mode controlling is a key process for designing an overmoded relativistic backward wave oscillator.Based on the numerical analysis and particle-in-cell simulation,the common-frequency high-order mode competition and output mode controlling of an overmoded RBWO with a wide-gap reflector are studied.It indicates that the high-order mode is mainly originated from the reciprocal mode conversion and excitation in the RF structures,which can be restrained and controlled by optimizing the sensitive parameters,reducing the conversion factor from fundamental mode to high-order one and adjusting the RF phases of different modes that are reflected back to the beam-wave interaction region from the cathode plate.Finally,a beam-wave conversion efficiency of 40% and an output TM01 mode purity of 98% are obtained at frequency of 9.87 GHz from the concerned overmoded RBWO.