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Smithers, Brian William George Dudley (1964) Measurements of electron density in gas discharge plasmas. Masters thesis, Northern Polytechnic.
Several methods of measuring electron densities in the positive column of a glow or arc discharge in nitrogen have been investigated. The limitations of an early theory of ion collection by probes are discussed and recent treatments put forward to deal with such difficulties are considered.
Experimental results with such probes are compared with those from a simple drift velocity-discharge current method.
Electron energy distribution curves obtained using Druyvesteyn's analysis show that the plasma electrons have a non-Maxwellian energy distribution. Total electron densities were calculated by summation of the areas under the distribution curves. The curves suggested that two groups of electrons were present and when, under some conditions, there groups combined to give an approximation to a Maxwellian distribution of energies a greater consistency between these results and the others was found.
Some probe experiments were made with probes in a high frequency discharge and good agreement was found between these experiments and those referred to above.
A method based on entirely different principles is that given by Persson. His theory relates the change in impedance of a solenoid enclosing the column to the electron concentration in the plasma. The experiments described show how plasma noise raised an insurmountable obstacle to measurements being made by this method in the positive column of the present discharge.
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