Neutral gas temperature measurements of a radio frequency micro-thruster

A radio frequency (13.56 MHz) capacitively coupled cylindrical argon plasma discharge was analysed using optical emission spectroscopy (OES) for various powers and pressures in the ranges 10 W to 40 W and 0.5 Torr to 5 Torr. Trace amounts of nitrogen were added to the discharge to estimate the temperature of the neutrals using rovibrational band matching of the 2nd positive system of nitrogen and the 1st negative system of nitrogen ions. Comparing simulated computer generated spectra of these bands to experimentally measured spectra determined the rotational and vibrational temperatures of the nitrogen, from which the temperature of the neutrals was inferred by assuming the rotational temperature was the same as the neutral gas temperature.