Results of investigation of propagation of perturbations in thermal plasma jet were used for determination of basic plasma jet characteristics. Fluctuations of plasma radiation in plasma jet generated in water plasma torch were recorded using system of photo-diodes with high frequency response.
Several types of fluctuations were identified within the jet with various velocities of propagation in the plasma. Strong perturbations were induced by the movement of anode attachment along the electrode surface in a restrike mode. A
production of distinct perturbation was observed in the point of creation of new anode spot by a restrike. This perturbation propagates within the plasma from the point of the restrike with the velocity of sound. From the measured velocities of perturbations a plasma velocity and temperature were evaluated assuming equilibrium plasma properties calculated under the assumption of existence of
local thermodynamic equilibrium. The resulting temperature agrees well with the temperature measured by an emission spectroscopy.