Breakdown in Air Produced by High Power Microwaves

The air breakdown driven by the high-power microwave radiated from the circular waveguide is investigated using the 2-D fluid model. We focus on the case of the air pressure higher than 100 torr, and therefore neglect the electron diffusion loss to the wall in the fluid model. A proper numerical scheme for the finite-difference time-domain method is developed to solve the fluid model. The results show that the air breakdown mainly occurs near the dielectric window due to the high electric field, and the generated nonuniform plasma causes significant attenuation in the radiated field. The wave reflection by the air plasma, far larger than the plasma absorbtion, attenuates the transmitted power significantly at low pressures, while at high pressures, the plasma absorbtion plays a major role in the transmitted power loss. The accuracy of the fluid model is validated by comparing with the reported experimental results.