Optical characterization of a high speed plasma's electromagnetic properties

Abstract

Very Low Frequency (VLF, 3-30kHz) and Low Frequency (LF, 30-300kHz) radio waves are useful due to their ability to travel around the world in the Earth-Ionosphere waveguide and excellent skin depth penetration into conductors. However, generation of these waves is limited due to the fact that their wavelengths are hundreds of meters to kilometers long. A recently proposed antenna concept known as VAIPER involves an antenna with timevarying conductivity. The antenna’s properties need to be varied at nanosecond timescales. This time-varying concept can be realized at low power with COTS components, but high speed switches cannot handle high power. A plasma is a conducting media with electrical properties that can be varied rapidly while handling high current flow. Antennas made from plasma have been constructed and tested in the past, but not with rapidly time-varying conductivity in mind. To determine a plasma’s viability as an antenna, its electromagnetic properties must be measured. Conventional plasma analysis techniques do not resolve variations in plasma at the desired speeds. The objective of the research in this thesis is to develop techniques to analyze a plasma column’s electric properties as it is ionized and de-ionized on the nanosecond timescales. Optical techniques are used to determine the time-varying conductivity of rapidly pulsed plasma. The conductivity measurements fed into a basic propagation model to determine whether the experimental plasma columns can support the VAIPER scheme.