Radio Science

Laboratory chamber experiments exploring the potential use of artificially ionized layers of gas as a Bragg reflector for over-the-horizon signals

Authors

  • S. P. Kuo,

  • Y. S. Zhang,

  • M. C. Lee,

  • Paul Kossey,

  • Robert J. Barker


Abstract

A set of parallel plasma layers is generated by two intersecting microwave pulses in a chamber containing dry air at a pressure comparable to the upper atmosphere. The dependence of breakdown conditions on the pressure and pulse length is examined. The results are shown to be consistent with the appearance of tail erosion of microwave pulse caused by air breakdown. Bragg scattering experiments, using the plasma layers as a Bragg reflector, are then performed. Both time domain and frequency domain measurements of wave scattering are conducted. The experimental results are found to agree very well with the theory. Moreover, the time domain measurement of wave scattering provides an unambiguous way for determining the temporal evolution of electron density during the first 100 μs period. A Langmuir double probe is then used to determine the decay rate of electron density during a later time interval (1 to 1.1 ms). The propagation of high-power microwave pulses through the air is also studied experimentally. The mechanisms responsible for two different degrees of tail erosion have been identified. The optimum amplitude of a 1.1 μs pulse for maximum energy transfer through the air has been determined.

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