利用傅里叶级数展开,给出了一种求解梯形慢波结构表达式的方法。通过数值模拟,研究了级数展开次数对求解精度的影响。当级数为10阶时,线型拟合而成的结构与原结构吻合较好。利用此表达式数值求解了色散方程,得到两个最低阶模quasi-TEM模和A 模。分析了为实现电子束与quasi-TEM模的-1次空间谐波相互作用慢波结构参数所需满足的条件,并指出利用此条件下纵向电场具有表面波的特点可实现横向模式选择。采用S参数理论研究有限长慢波结构的纵向谐振特性,提出在同轴慢波器件中加入同轴引出结构可减少所需慢波结构周期数,这不但使器件结构更为紧凑,还可避免纵模竞争从而提高器件效率、稳定产生微波频率。在此基础上设计了一种L波段同轴相对论返波振荡器,采用KARAT 2.5维全电磁粒子模拟程序研究了器件内束-波作用的物理过程。模拟结果表明,该器件具有径向尺寸小、束-波作用效率高的特点。在电子束能量700 keV、电子束流11.5 kA的条件下,器件在频率1.6 GHz处获得较高的微波输出,饱和后微波的平均功率达2.60 GW,平均效率约为32.3%。

The method for calculating the expression of the trapezoidal corrugation slow-wave structure (SWS) is studied in detail,which uses Fourier series expandedness. The dispersion curves of the two lowest symmetry TM0n waves are obtained with numerical calculation. Moreover,longitudinal resonance properties of the finite-length coaxial SWS are investigated with the S-parameter method. It is proposed that the introduction of a well designed coaxial extractor to slow-wave devices can reduce the period-number of the SWS,which not only can make the devices more compact,but also can avoid destructive competition between various longitudinal modes. Based on the theoretical study,a compact L-band coaxial relativistic backward wave oscillator is designed using the 2.5 D particle simulation code. Simulation results show that for an electron beam of 700 keV and 11.5 kA,the high-power microwave of coaxial TEM mode is generated with an average power of 2.60 GW after saturation and a frequency of 1.6 GHz,and a power conversion efficiency of 32.3% in the duration of 30 to 60 ns.