| High-power microwave pulse-compression techniques are used to generate 2.856 GHz pulses which are propagated in a TE(,10) mode through a gas filled test section of waveguide, where the pulses interact with self-generated gas-breakdown plasmas. Pulse envelopes transmitted through the plasmas, with durations varying from 2 ns to greater than 1 (mu)s, and peak powers of a few kW to nearly 100 MW, are measured as a function of incident pulse power and gas pressure for air, nitrogen, and helium. In addition, the spatial and temporal development of the optical radiation emitted by the breakdown plasmas are measured.;For transmitted pulse durations (GREATERTHEQ)100 ns, good agreement is found with both theory and existing measurements. For transmitted pulse durations as short as 2 ns (less than 10 rf cycles), a two-dimensional model is used in which the electrons in the plasma are treated as a fluid whose interactions with the microwave pulse are governed by a self-consistent set of fluid equations and Maxwell's equations for the electromagnetic field. The predictions of this model for air are compared with the experimental results over a pressure range of 0.8 torr to 300 torr. Good agreement is obtained above about 1 torr pressure, demonstrating that microwave pulse propagation above the breakdown threshold can be accurately modeled on this time scale. |
