High power microwave window flashover at atmospheric pressures

One of the major limiting factors to the transportation of high power microwave (HPM) radiation is the interface between dielectric-vacuum or even more severely between dielectric-air if HPM is to be radiated into the atmosphere. Surface flashover phenomena which occur at these transitions severely limit the power levels which can be transmitted. It is of major technical importance to predict surface flashover events for a given window geometry, material and power level. When considering an aircraft based high power microwave platform, variances in the operational environment corresponding to altitudes from sea level to 50,000 feet (760 torr to 90 torr) are also important. The test setup is carefully designed to study the influence of each atmospheric variable without the influence of high field enhancement or electron injecting metallic electrodes. Diagnostic equipment allow for the measurement of power levels, luminosity and optical emission spectra with resolution in the nanosecond time regime.

Experimental results on HPM surface flashover are presented, including the impact of gas pressure and humidity, and the presence of UV illumination, along with temperature analysis of the developing discharge plasma and temporally resolved images of the flashover formation in air and nitrogen environments. These results are compared with literature data for volume breakdown in air, with discussion of the similarities and differences between the data.