A method is presented to determine the electron temperature in a low pressure argon plasma using emission spectroscopic measurements and a collisional radiative (CR) model. Absolute line intensity measurements are made in order to construct the atomic state distribution function. In addition to the excited states, the ground state density is also taken into account. Because of this, the excitation temperature can be determined with high precision. A CR-model has been used to determine the degree of equilibrium departure and to obtain the relationship between the excitation temperature and the electron temperature. This method is applied to a microwave plasma which has been generated inside a quartz tube using a surfatron device. The densities of argon levels close to the continuum are used to get an estimated value of the electron density. These values are used as input data for the CR-model. For an argon pressure of 6 mbar, the 4p level densities vary between 8 × 1014 and 6 × 1015 m−3. Using the estimated values for the electron density, between 2 × 1019 and 3 × 1019 m−3, the electron temperature was found to range between 1.15 and 1.20 eV. An extensive error analysis showed that the relative error in the electron temperature is less than 6%.

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A method for the determination of the electron density (ne) using the continuum radiation is presented. The radiation is calibrated with a standard tungsten ribbon lamp and thus expressed in absolute units. This method is applied to a microwave-induced argon plasma, created by a surfatron (2.45 GHz), for which the standard settings are: wavelength region at 648 nm, power of 60 W, pressure of 15 mbar, gas flow of 70 sccm and axial distance from the launcher of 3 cm. Due to the low degree of ionization, the influence of electron–ion interactions can be neglected; the radiation is predominantly generated by free–free interactions between electrons and atoms. The method provides the electron density values in the order of 1019 m−3 for different plasma settings. It is observed that the measured ne follows the well-known trends—it decreases in the direction of the propagating surface wave and increases with power.

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