Microwave Corona Breakdown In Rf Devices

The main physical properties of microwave corona breakdown in gases in the presence of inhomogeneous electric fields are investigated using numerical calculations of the continuity equation for the density of free electrons. In particular, the interplay between diffusion and attachment in redistributing electrons from high field regions to low field regions and the concomitant effect on the breakdown threshold is studied for different examples of the variation of the electric field strength. The results give a clear physical picture of the dependence of breakdown electric field on pressure with two complementary limits; a high pressure limit with a localized breakdown plasma confined to the high field region and a low pressure limit determined by the properties of the low field region only and a breakdown plasma extending over the entire volume of the rf device. A comparison between results for the critical microwave breakdown field as obtained by numerical calculations and experimental results in a microwave cavity show very good agreement.