We report on investigations of gas metal arc welding plasma operated in pure argon and in a mixture of argon and CO 2 at a dc current of 326 A. The spatially resolved electron densities and temperatures were directly obtained by measuring the Stark widths of the Ar I 695.5 nm and Fe I 538.3 nm spectral lines. Our experimental results show a reduction of the plasma conductivity and transfer from spray arc to globular arc operation with increasing CO 2 concentration. Although the electron density n e increases while approaching the core of the plasma in the spray-arc mode, a drop in the electron temperature T e is observed. Moreover, the maximum T e that we measure is about 13 000 K. Our experimental results differ from the Haidar model where T e is always maximum on the arc axis and its values exceed 20 000 K. These discrepancies can be explained as a result of underestimation of the amount of metal vapours in the plasma core and of the assumption of local thermal equilibrium plasma in the model.

Noisy and spectrally poorly resolved molecular emission spectra of the 306.357 nm OH band were employed for evaluation of the rotational temperature in different plasma sources, in the temperature range 300 - 6000 K, when an apparatus function of a recording system is unknown. The described method is based on a comparison of experimental data with a theoretical spectrum. The following plasma sources are examined: a recombining jet of plasma torch, an atmospheric pressure glow discharge, a surface ionized wave device and a gliding arc. The temperatures of these weakly ionized plasmas, measured from the OH spectra, are in good agreement with temperatures obtained by using other techniques: thermocouples, tungsten wire resistance measurements and other spectroscopic methods. The results show that the OH spectra are very useful for temperature measurements of non-equilibrium plasmas.

Gliding arc discharges are the subject of renewed interest in applications to a variety of chemical reactions. A gliding arc is created by a weakly ionized gas flowing between two electrodes. The reacting gas introduced at the base blows the arc column upwards. These devices are used in industry mainly for decontamination and general gas treatment. Either ac or dc can be used as the power supply. In order to analyze gliding arc motion, a multi-shot camera was designed with a very short exposure time. A high-voltage dc arc is studied and a simple theoretical model is given which enables determination of the conduction radius and axial temperature.