Optical and Probe Diagnostics for Tabletop-Scale Inductively Coupled Plasma Tunnels

Optical emission spectroscopy (OES) and a Langmuir probe have been applied to two tabletop-scale inductively coupled plasma (ICP) tunnels at the Magnetoaerodynamics and Aerospace Plasmas Laboratory at the University of Colorado Boulder (CU-MAPLAB) to measure various flow and plasma properties in pure argon plasma and pure air plasma travelling at supersonic speeds. Experimental spectra and current-voltage characteristics were obtained for a combination of input radio-frequency power levels, test gas flow rates, and axial measurement locations. The Boltzmann plot method and spectral fitting were used to estimate electronic excitation, vibrational, and rotational temperatures. Various probe theories were utilized to comparatively measure electron temperatures, electron number densities, and ion number densities while also observing electron energy distribution functions.