An Application of Spectroscopic Techniques to the Measurement of Electron Density and Temperature in a Brush Cathode Plasma

Date of Award

Summer 8-1971

Document Type


Degree Name

Master of Science (MS)



Committee Director

James L. Cox

Committee Member

R. P. Chopra

Committee Member

Jacob Becher

Call Number for Print

Special Collections LD4331.P48P37


A brief review of the Langmuir probe, microwave and spectroscopic techniques most commonly used to make measurements .of plasma electron temperature and density is presented. Of these various methods, certain spectroscopic methods are applied to the measurements of electron density and temperature in a helium brush cathode plasma. The density measurement is based on the manner in which a series of Stark broadened spectral lines merges into an apparent continuum before the normal series limit is reached. This approach met with only limited success in that the density could be determined only by extrapolating the data obtained. Primarily because of problems associated with the plasma source geometry, the intensities of the spectral lines near the modified series limit were too low to allow them to be ~ recorded, thus necessitating this extrapolation. Procedures used to increase the signal to noise ratio so as to render individual lines more distinguishable are discussed. Included in this discussion is a description of an amplifier circuit which was designed for this purpose and which proved useful. Estimates are given to show the kind of source modifications which would allow a more successful use of this approach to the problem of measuring the plasma electron density in the plasma source studied. The electron temperature was measured by the use of a method employing the measured ratio of the intensities of selected spectral lines.


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