多载波微放电阈值的粒子模拟及分析

摘要

多载波微放电阈值的准确分析对于空间大功率微波系统的长期可靠性至关重要.近年来,一种源于多载波包络周期间少量剩余电子累积的"长周期"微放电机制引发广泛关注.国内外研究者普遍认为,相对源于单个周期内电子累积的"周期内"微放电,"长周期"微放电应该被优先激发、具有更低的阈值.但依据长周期微放电判据分析所得的阈值显著高于实验结果.针对这一问题,本文采用与实验系统可比拟的微放电判据,在相同多载波信号激励、相微波部件条件下,对微放电的演化过程进行了粒子模拟,分析了多载波微放电、特别是周期内微放电的行为特性和发生条件,有效地解释了实验结果.本文的粒子模拟结果表明,给定微波部件被优先激发的多载波微放电类型取决于载波频率的配置,长周期微放电并非一定被优先激发,这是导致基于长周期微放电判据分析所得阈值显著高于实验结果这一问题的原因所在.以上结论对于空间大功率微波部件的多载波微放电全局阈值评估和抑制设计具有指导意义.%The multicarrier multipactor is a phenomenon that can be observed in vacuum environment due to the effect of secondary electron emission. Accurate analysis of the threshold of multicarrier multipactor is crucial for the long-term reliability of high-power spaceborne microwave system, and therefore it has been attracting more and more interests in fields of high-power microwave community, plasma physics and aerospace engineering. Recently, a new mechanism of multicarrier multipactor, termed "long-term" multipactor, induced by sustained accumulation of residual electrons between successive envelope periods of multicarrier signals has received much attention. Comparing with the "single-event" multipactor induced by the electron accumulation inside a single envelop period, researchers tend to believe that the threshold of the long-term discharge should be lower. However, recent experimental results show an opposite conclusion. In this work, in order to investigate the contradiction between the experimental and theoretical studies on the thresholds of multicarrier multipactors, particle simulations are used to simulate the evolution process of the multicarrier multipactor under the same conditions and judgement criterion. The behavioral characteristics and occurrence condition for multicarrier multipactors, especially the single-event ones, are analyzed based on a power scanning analysis, and the conflicting results are effectively explained. Our simulations show that if the evolution process of a multipactor can be divided into three phases, i.e., establishment phase, critical phase and saturation phase, the experimental reflection coefficient can be corresponding to the reflection coefficient simulated in the critical phase. The simulation results indicate that the type of the multipactor discharge would depend on the configuration of multicarrier signals. For multicarrier signals with relatively narrow bandwidths, single-event multicarrier multipactors could occur in the first place at a lower threshold power. Therefore, the threshold of a long-term discharge is not necessarily lower than that of a single-event one. This conclusion is important for estimating and suppressing the multicarrier multipactors in the design of high-power spaceborne microwave components.