High-power microwave breakdown of dielectric interfaces

A project to study the electrical breakdown of microwave windows due to high-power pulsed microwave fields was undertaken at Texas Tech University. The pulsed power equipment was acquired from the Air Force Weapons Laboratory (now Phillips Laboratory) in Albuquerque, NM, refurbished and redesigned as necessary, and serves as the high-power microwave source. The microwaves are used to test various vacuum to atmosphere interfaces (windows) in an attempt to isolate the mechanisms governing the electrical breakdown at the window.

Windows made of three different materials and of three basic geometrical designs were tested in this experiment. Additionally, the surfaces of two windows were sanded with different grit sandpapers to determine the effect the surface texture has on the breakdown. The windows were tested in atmospheric pressure air, argon, helium, and to a lesser extent sulfur-hexafluoride. Estimates of the breakdown threshold in air and argon on a Lexan window were obtained as a consequence of these tests and were found to be considerably lower than that reported for pulsed microwave breakdown in gases. A hypothesis is presented in an attempt to explain the lower breakdown electric field threshold. A discussion of the comparative performance of the windows and an explanation as to the enhanced performance of some windows is given.