Examination of the shock wave regular reflexion phenomenon in a rarefied supersonic plasma flow

The flow properties of a low-pressure weakly ionized supersonic argon plasma jet are examined using Fabry-Perot interferometry and laser induced fluorescence spectroscopy. The flow velocity and equilibrium temperature measured at the torch nozzle exit are in close agreement with computational fluid dynamics calculations. The model also predicts the plasma flow to be in a rarefied regime. Departure from thermal equilibrium is indeed observed behind the nozzle where the parallel temperature differs significantly from the perpendicular temperature. The development of the axial velocity component along the jet center stream line reveals the occurrence of the shock wave regular reflexion phenomenon: No Mach disk is formed and the flow experiences successive supersonic-to-supersonic transitions before reaching a subsonic regime. Shock wave regular reflexion is in fact favored under our experimental conditions since the speed ratio is high and the rarefaction degree is pronounced at the nozzle exit