Measurements of temperature and electron number density measurements have been carried out on a plasma plume under various pressure conditions (p = 1-0.3 bar) using emission spectroscopy. The anode nozzle used does not generate a shock wave or an expansion-compression zone. Ar- (1%) is used as the plasma gas. Temperature values are obtained from various lines of neutral argon. Electron number densities are obtained from the Stark-effect broadening of the 486.1 nm H line and the continuum measurements. Measurements of temperature and density profiles reveal the general features of a low-pressure plasma jet, namely relatively low temperature and long heating zone of the expanded jet. The LTE criterion is satisfied at higher pressures ( bar). Deviations from ionization equilibrium occur at lower pressure. The variation of excited neutral argon and states has been studied for lower pressures. tends to be overpopulated compared with .

The Fast Fourier Transform method has been applied to light and voltage fluctuations in a low power (<5 kW) dc plasma torch burning in argon. The influence of the gas flow on the development of turbulence in the plasma jet has been studied. The temporal and spatial non-homogeneities observed in the plasma flow have been linked to the dynamic processes in a dc plasma torch.

The fluctuations generated by arc root motion have been used to determine the velocity in a plasma jet. The phase angle relations resulting from time variations of light intensity profiles taken simultaneously across different sections of the plasma have been used to determine the velocity for different operating conditions of the dc torch. The experimental results have been compared with the theoretical predictions of a 2D MHD model of the dc plasma torch. The experimental and theoretical values appear to agree with a maximum deviation in the 5-10% range.

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