三种同轴双波纹周期慢波结构对比研究

Comparative research on three types of coaxial double-corrugation periodic slow-wave structures

利用Fourier级数展开法,给出了任意几何结构的表达式的求解方法.通过数值计算,对比分析了余弦、梯形和矩形波纹慢波结构(slow-wave structure,SWS)的色散特性.根据S参数理论,研究了这三种SWS纵向模式选择的特性,提出了在同轴慢波器件中加入同轴引出结构,可减少所需SWS周期数,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.进一步通过KARAT2.5维全电磁粒子模拟程序,探讨了分别采用三种SWS的相对论返波振荡器(backward-wave oscillator,BWO)的束-波作用的物理过程,设计了一种紧凑型、吉瓦级、同轴L波段BWO,分析了不同形状SWS的选取原则.在此基础上,开展了初步实验研究:在二极管电压为670kV,电子束流为10.7kA,引导磁场为0.75T的条件下,输出微波峰值功率约为1.02GW,微波波形半高宽为22ns,功率转换效率约为14.2%,频率为1.61GHz.

The method for deducing expressions of arbitrary geometrical structures is studied in detail by using the Fourier series expansion.The dispersion curves of the slow-wave structures（SWSs） with the cosinoidal,rapezoidal and rectangular corrugations are obtained by numerical calculation.Moreover,the 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 help to reduce the period-number of the SWS,which not only can make the devices more compact,but also can avoid the destructive competition between various longitudinal modes.Furthermore,a compact L-band coaxial relativistic backward wave oscillator（RBWO） is investigated and optimized in detail with particle-in-cell（PIC） methods（KARAT code）.In the preliminary experiments,the measured microwave frequency is 1.61 GHz,with a peak power level of above 1.02 GW,when the diode voltage is 670 kV and the current is 10.7 kA.The pulse duration（full-width at half-maximum） of the radiated microwave is 22 ns.