Fundamental properties of a microwave induced argon plasma

Surrey, E. (1987) Fundamental properties of a microwave induced argon plasma. Doctoral thesis, Polytechnic of North London.


The behaviour of a microwave excited electrodeless argon discharge is investigated at pressures between 0.02 and 6.00 mbar. Spectroscopic measurements of twenty one emission lines of the argon I spectrum and seven lines of the argon II spectrum are combined with microwave impedance and Langmuir probe measurements. The population densities of some seventeen levels of the argon atom are evaluated and the results analysed in terms of a collisional-radiative recombination model due to Fujimoto. The atomic system is shown to be in the saturation phase above the 5p level and the population coefficients for seven levels of the argon atom are determined.

Values of ion density and electron temperature are derived from probe measurements. The former are compared with values of electron density derived from impedance measurements and it is shown that the condition of electrical neutrality is not valid in this plasma. Ion loss to the walls of the discharge tube is demonstrated to be a major contributor to the non-neutrality of the plasma.

The effect of a double Maxwellian distribution of electrons upon the double floating probe characteristics is investigated. A pair of equations is derived to describe the characteristic under this condition and the results are shown to fit an observed, but previously undescribed, form of characteristic. The behaviour of the characteristic for different ratios of electron temperature and electron density of the two distributions is examined and it is shown that careful consideration must be given to the interpretation of double floating probe characteristics to avoid ambiguous results.

The effect of microwave power on the population densities of the argon atom and ion, the electron temperature and the electron and ion densities is examined. It is shown that power and pressure are not independent variables and the consequences of this for the analysis of the data is discussed.

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