Window Flashover Initiation under Pulsed Microwave Excitation

Surface flashover development at the output window of high power microwave (HPM) systems presents a major limitation to the power densities and pulse lengths transmitted through these interfaces. As a result, developing a physical model accurate in predicting surface flashover initiation is of prime interest. A Monte-Carlo type electron motion simulation has been developed to estimate the delay time from initial electron to flashover. Although this approach has shown reasonable agreement with experimental results, the process yielding the initial seed electron(s) was neglected in the model, primarily due to the lack of quantitative and qualitative information on seed electron production. For instance, computational efforts investigating seed electron production via collisional detachment from negative oxygen ions have shown that while effective at DC, the collisional detachment model cannot remain a likely contributor of electrons at high frequencies (Gt ~5 GHz). The key parameters impacting high power microwave surface flashover will be discussed and presented along with continued investigation into the statistics of possible seed electron sources, including trace contaminates present in the gas or on the dielectric surface.