Krypton-Tagging Velocimetry in a Low-Speed Atmospheric-Pressure Inductively-Coupled Plasma Plume

As part of an ongoing project to develop an exascale, multi-physics simulation of an inductively-coupled plasma (ICP) torch, measurements of the plasma plume velocity are needed for validation purposes. The 50 kW ICP torch studied, operates on argon and exhausts to ambient air at low-speed and with a temperature of about 6000 K. Pitot-static probe measurements have been made in the plasma using a water-cooled probe, however the cooling necessitates a relatively large diameter probe that introduces an unquantified blockage effect and converting to velocity requires assumptions about the flow that may not be valid. The high temperatures also make many common non-intrusive techniques such as PIV or MTV difficult to implement. Krypton Tagging Velocimetry (KTV) was employed and successfully used to measure velocity in an atmospheric pressure argon plasma plume. KTV is a two-step technique in which a metastable electronic state of krypton is first populated with one laser pulse. Once populated, this metastable state is probed with a separate laser pulse after a known delay to produce a line of fluoresence that has convected with the flow. Fluoresence was detected out to 20 µs of delay. The various challenges in making such measurements will be discussed.