Spatially and temporally resolved characterization of an air breakdown plasma using A 110 GHz, 1.4 MW gyrotron

Summary form only given. We present new results on air breakdown using a 1.4 MW, 110 GHz gyrotron operating in 3 microsecond pulses. The linearly polarized beam is focused to a 3.2 mm diameter spot size. The resulting breakdown plasma spontaneously forms a two-dimensional array of filaments or streamers, oriented along electric field lines, that propagate toward the source¹. Making use of a fast gating ICCD, we have documented the formation and dynamics of the array with 2 nanosecond time resolution. In addition, a two-wavelength laser interferometer, operating at 532 and 635 nm, has been used to make spatially and temporally resolved electron density measurements of the plasma array, again with nanosecond time resolution. Measurements are made as a function of incident microwave power and ambient air pressure. Microwave power is varied from the breakdown threshold up to 1.4 MW. Ambient air pressure is varied between 25 and 700 Torr.