ABSTRAKT

A dc hybrid Ar-water plasma torch attached to a vacuum vessel was used for the experiment. Plasma optical radiation from the jet was recorded by a fast CCD camera adapted for acquisition of image series containing 8 pictures of the plasma jet with time intervals 4 μs and exposure time 200 ns. The conditions for the onset of turbulence in the plasma jet were varied by changing the pressure in the vacuum vessel between 10 and 80 kPa. The analysis of the acquired images was based on subtraction of matrices representing succeeding pictures in the series. This method reveals turbulent structures characterized by increasing or decreasing luminosity moving along the flow. The evaluation of the results included statistical analysis of the number, size and velocity of the detected structures. The statistical distributions of these quantities approach Gaussian shapes at low pressures. A significant transition in the flow behaviour occurs between 30 and 40 kPa.