Identification of dynamic patterns and their velocities in thermal plasma jets

The paper presents a new method for identification of dynamic structures in a plasma jet using CCD camera records of its radiation and shows also possible application of the method for evaluations of plasma velocity. The evaluation of CCD images is based on the subtraction and correlation analysis of succeeding pictures in the recorded sequence. The results show that plasma jets include various types of structures moving downstream. The quantity, evolution and velocity of the detected patterns depend on the input gas flow rate. The measurements included also parallel records of local plasma jet radiation detected by photodiode arrays. The evaluation of the photodiode records in the form of long time series was founded upon the fast Fourier transform, especially on the analysis of phase angle shifts between signals coming from photodiode pairs situated along the plasma flow. These phase shifts yielded plasma flow velocity that was compared with the velocities of structures identified by the analysis of CCD camera images.