Surface flashover under RF and unipolar excitation at atmospheric conditions

In vacuum environments surface flashover events driven by RF (f < 10 GHz) and unipolar excitation have been shown to have virtually identical dominant mechanisms. Similarities between RF (representing high-power microwave window breakdown on the high pressure side) and unipolar surface flashover are expected in an atmospheric environment as well. Extensive testing has already been completed for both DC and pulsed unipolar flashover with several dominant processes identified. Further testing with a setup capable of HPM driven surface flashover are conducted to identify similar dominant processes.

The two separate experimental setups, utilized to investigate both unipolar flashover and RF window flashover under atmospheric conditions, enable controlling excitation, temperature, pressure, humidity, and type of gas present, all under similar electric field�surface geometry. In order to ensure the conditions are as matched as possible, the local electric field at the flashover initiating points has been numerically calculated in detail for all test geometries. In addition a Monte Carlo type electron motion simulation program was created to further isolate the individual processes.

For both RF and unipolar pulsed excitation, the flashover dynamics are changed by the application of UV light to the dielectric surface. A UV pre-pulse has a distinct impact on the arc�s path and a tendency to decrease the hold-off electric field. The effect of humidity on the hold-off electric field for both pulsed unipolar and RF excitations, along with temporally resolved emission spectroscopy of the flashover event, are discussed.