Air breakdown in an increasing SHF field

The non-electrode high-pressure air breakdown in the standing wave focus of the high-quality quasi-optical two-mirror resonator operated by single SHF pulses is studied. The breakdown under experimental conditions proceeded on the field pulse front in the resonator. The field level whereby the breakdown took place essentially exceeded the critical one and under all constant conditions had statistical spread in the successive pulses. It is shown that the excess of the breakdown threshold field fixed in the experiments, over the critical one, is conditioned by the field growth in the resonator during the development of the discharge plasmoid formed in the breakdown process, and by the incidental character of appearance in the gas of the electron initiating the breakdown