Date of Award:

5-1989

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Electrical and Computer Engineering

Department name when degree awarded

Electrical Engineering

Committee Chair(s)

Kay D. Baker

Committee

Kay D. Baker

Committee

L. Carl Howlett

Committee

Frank Redd

Abstract

Electron density in a plasma can be measured by determining the plasma frequency. For 20 years this electron density measurement technique has been used with the plasma frequency probe. The purpose of this paper is to characterize, evaluate, and suggest improvements for this instrument. Although the current plasma frequency probe is a highly successful instrument for measuring absolute electron density in the ionosphere, several areas for improvement were found. These were in the radio frequency head and the voltage controlled oscillator. Currently, the plasma frequency probe is approximately 20% accurate in determining absolute densities around 1.5x104 electrons/cm3 but better than 5% accurate at densities greater than 1.5x105 electrons/cm3. The errors result from systematic instrument error that can be improved. A model for the plasma frequency probe is developed to help explain the dynamics of the instrument. The use of this model in choosing instrument components should solve the problems of frequency aliasing with the present instrument. Attempts to band limit the instrument above 700 hz have failed, resulting in a low slew rate, unexplainable by system modeling, dominating the system. Further analysis is suggested in several areas, including slew rate.

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