等离子体填充金属光子晶体慢波结构色散特性研究

Dispersion properties of plasma-filled metallic photonic crystal slow-wave structure

等离子体填充慢波器件为高效率、高功率真空电子微波源的发展提供了新的途径,但其仿真和理论都具有一定的难度.本文将通过轮辐天线加载激励信号的方法引入到等离子体填充金属光子晶体慢波结构(SWS)的色散特性仿真分析中,研究了慢波结构参数和等离子体密度对等离子体填充慢波结构色散特性的影响.结果表明,无等离子体填充时,通过轮辐天线加载激励信号方式得到的色散特性与其他方法差别不大;与已有结果对比表明,该方法适用于等离子体填充慢波结构的分析.为了减小轮辐天线对腔体谐振频率的影响,需要适当减薄轮辐天线的厚度,并尽可能缩短其与反射面之间的距离.天线的厚度越大越能激励慢波场,越小谐振模式越容易被激励;慢波结构周期膜片外半径和厚度对色散特性影响不大,周期长度和膜片内半径对色散特性影响较大;频率和相速色散曲线随等离子体密度上升而整体向高频区移动;等离子体填充对低频模点的影响要大于对高频模点的影响;对于慢波器件,需要选择高频模点工作模式,以减少腔的尺寸并降低电子注的初速度.

Plasma-filled slow-wave devices provide a new way to develop high efficiency and high power vacuum-electron microwave sources, but their theoretical analysis and simulation is difficult. This paper introduces the wheel spoke antenna to excite signals for analyzing the dispersion characteristics of resonant cavity with plasma-filled metallic photonic crystal slow-wave structure （SWS）. Influences of parameters of the SWS and plasma density on dispersion characteristics of the SWS are studied. Results show that there is little difference in dispersion characteristics obtained by wheel spoke antenna excitation of signals and other methods without plasma filling. When plasma fills in the SWS, the frequency of zero mode is consistent with the previous results obtained by other methods. Hence, both the results with and without plasma filling demonstrate that the wheel spoke antenna signal-excitation method is effective. Moreover, decreasing the thickness of wheel spoke antenna properly and the distance between the antenna and reflection surface of the metal plate can reduce the wheel spoke antenna influence on the cavity resonance frequency. Furthermore, thicker antenna can excite the slow wave field easily, while thinner antenna can excite the resonant mode easily. Besides, the outer radius and thickness of the SWS plate have little influence on the dispersion characteristics, while the period length and the inner radius of the SWS plate have greater influence on the dispersion characteristics. In addition, the dispersion curves of frequency and phase velocity will move to higher frequency regions with the increase of plasma density. Further, the influence of plasma filling on low-order modes is greater than that on higher order modes. It is also found that the higher-order mode operation can reduce the size of cavity and the velocity of the electron beam.