Parametric study of a vortex-enhanced supersonic inductively coupled plasma torch

Radio-Frequency (RF) Inductively Coupled Plasma (ICP) torches have applications ranging from materials processing and gas conversion to electric space propulsion. In this work, we study a novel RF ICP torch design that includes a supersonic nozzle and a gas injection configuration generating bidirectional vortex flows. The ICP plasma is characterized using optical emission spectroscopy, calorimetry, and electrical circuit measurements to determine the electron density and gas temperature, as well as performance metrics such as the torch thermal efficiency and specific enthalpy. Experiments are performed for gas pressures and argon mass flow rates up to 80 kPa and 450 mg/s respectively, and RF powers between 200-1000 W. A primary parametric study variable is the supersonic nozzle throat diameter, which is varied between 1.5-4 mm. As the nozzle throat diameter is increased, the electron density decreases and the neutral gas temperature increases for a given mass flow rate and RF power. The nozzle size has a significant effect on the maximum torch thermal efficiency, which increases from approximately 20% to just above 65%. This enhanced performance occurs because of reduced heat losses to the torch walls and demonstrates the shielding effect enabled by the vortex flow fields, as well as the important influence of nozzle design.