Microwave Breakdown in Air, Oxygen, and Nitrogen

The electric fields required to initiate breakdown in air, in nitrogen, and in oxygen have been measured at frequencies in the $L$, $X$, and $K$ bands, in a number of resonant cavities. The sizes of the cavities varied greatly so that the relative roles of diffusion and attachment in the breakdown process could be studied. The pressures at which measurements were made varied from approximately 0.01 to 100 mm Hg, corresponding to atmospheric breakdown at altitudes from 15 to 80 km. Pulsed power measurements were made at all frequencies and continuous wave (cw) measurements were made at $X$ and $L$ bands. A theoretical analysis provides a scheme for predicting pulsed and cw breakdown in air for frequencies from 100 Mc/sec to 100 kMc/sec, for pressures corresponding to altitude variation from 0 to 100 km.