In this study, two complementary techniques of diagnostic are used to study the properties of a supersonic HF plasma flow: namely, an enthalpy probe measurement and a flow visualization. A PL-35 induction plasma torch operating with three convergent-divergent Laval-type nozzles generates the plasma: a Mach 3.0 velocity water-cooled (wc) nozzle, a Mach 1.5 velocity wc nozzle and a Mach 2.45 velocity radiation-cooled (rc) nozzle. The plasma plate power is fixed at 20 kW and chamber pressure varies between 1 and 10 kPa. The plasma gas is argon and its flow is fixed at 60 slpm. The enthalpy probe profiles of local enthalpy and stagnation pressure are measured, from which, temperature, velocity and Mach number are obtained. The effect of nozzle design on plasma properties is investigated. The RC nozzle creates a plasma jet hotter with a steeper thermal profile and a higher mean velocity than the wc nozzle. The enthalpy probe calculations imply the assumption that the static pressure of the flow is similar to the chamber pressure. Experimental results show that this assumption is still applicable in the jet fringes, but its value changes strongly along the radial and axial axis. Also, photographs of the oblique shock wave in front of a cone in the plasma flow allow the approximation of the flow Mach number produced by a Mach 1.5 velocity wc nozzle. Its approximate value is 2.0, which is higher than predicted.

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