Short pulse High Power Microwave surface flashover

Abstract

High Power Microwave (HPM) surface flashover is investigated in order to gain a better understanding of this phenomenon and reduce the limitations it imposes on transmitted power levels. The experimental setup is designed to produce window flashover without the influence of a triple point. The HPM source for this testing is an experimental virtual cathode oscillator (vircator) capable of producing greater than 50 MW for 100 ns with an adjustable frequency from 3 to 5 GHz. This work builds on previous testing using a magnetron producing 5 MW for 4 μs at 2.85 GHz. The dominant modes of the vircator and magnetron are the circular TE <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</inf> and rectangular TE <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">10</inf> modes respectively, with the major electric field component in both setups normal to the direction of propagation, yielding comparable conditions. Due to the large differences in output power and pulse length, the two setups operate in different regimes and mechanisms may take on differing degrees of importance. The experimental setup permits study of factors including gas pressure, composition, temperature, and air speed. Diagnostic equipment allows the analysis of power levels with sub-nanosecond resolution. Experimental results are compared with data from literature, previous testing, and Monte Carlo simulations.