介质部分填充平行平板传输线微放电过程分析

本文主要研究了介质填充微波部件微放电随时间演变的过程,重点分析了介质微波部件微放电自熄灭机理.以介质部分填充平行平板传输线为研究对象,忽略空间电荷效应,采用自主研发粒子模拟软件模拟微放电过程,并将模拟结果与金属微波部件结果进行对比.结果表明,在一定功率下,金属微放电过程中电子数目呈指数形式增长,而介质微放电过程经历初始电子倍增后发生自熄灭现象,同时发现在电子数目即将下降为0时,介质表面的平均二次电子发射系数大于1或约等于1.另外,在上述模拟结果的基础上对微放电过程中介质表面积累电荷问题进一步分析,模拟结果表明,如果持续向微波部件内注入电子,介质表面的平均二次电子发射系数最终都约等于1.所得结论对研究复杂介质填充微波部件微放电的机理具有一定的理论指导价值.

Multipactor in parallel-plate transmission line partially filled with dielectric material

Due to the poor conductivity of the dielectrics, if an electron collides with the dielectric material, a charge will be deposited on the surface as a consequence of the secondary electron emission. Thus, the multipactor process in dielectric-loaded microwave devices differs from those in metallic devices. The objective of this paper is to study the self-extinguishing physical mechanism of the multipactor in parallel-plate transmission lines partially filled with dielectric layers by particle-in-cell simulation. The self-consistent field generated by the electrons in the simulation is assumed to be neglected, since there do not exist too many electrons in the self-extinguishing process. To illustrate the self-extinguishing phenomenon in a dielectric-loaded waveguide device, the strength of electric field in the vacuum area needs to be the same as that in a metallic device. When the input power is slightly higher than the multipactor threshold, the self-extinguishing phenomenon occurs after the initial electron multiplication while the number of electrons increases exponentially with the simulation duration in metallic device. Based on this fact, the physical mechanism of self-extinguishing phenomenon is investigated in detail. By analyzing the temporal evolution of the electrons and the average secondary electron yield (SEY), it can be concluded that the self-extinguishing phenomenon is caused by the electrostatic field generated by the charges deposited on the surface of the dielectric. Moreover, the average SEY of the dielectric tends to be one or greater than one when the number of electrons drops to nearly zero. Hence, it is necessary to further analyze the ability to continue accumulating charges on the dielectric surface when extra electrons are injected into the simulation region at the instant when the number of electrons is close to zero. For the former case, the charges deposited on the dielectric surface remain steady all along, while the charges reach to a stable state eventually as the number of injected electrons increases for the latter one. Both of them mean that the average SEY of the dielectric surface will be unity in the end. Since the electrostatic field generated by the charge deposited on the dielectric surface can reduce the risk of occurrence of multipactor, the electret material could be used in the design of the dielectric-loaded microwave devices to improve the multipactor threshold.