Determination of 915-MHz Atmospheric Pressure Air Microwave Plasma Torch (MPT) Parameters

The gas temperature, electron temperature, and electron density are critical parameters that affect microwave plasma chemistry processes in industrial applications. Using optical emission spectroscopy (OES), the gas temperature and electron density of a 915-MHz atmospheric pressure air microwave plasma torch (MPT) were investigated at various absorbed power levels and radial positions. In addition, the variation in the electron temperatures of 915-MHz atmospheric pressure argon microwave plasma filaments was analyzed as a function of the absorbed power. The experimental results showed that: 1) the absorbed power had little effect on the radial gas temperature or electron density; 2) the skin effect was present in the 915-MHz atmospheric pressure air MPT, where it causing caused hollowing in the center of the radial gas temperature distribution; 3) the electron density reached approximately $2\times10$ 13 cm−3 and was almost insensitive to variations in the absorbed power in the center of the 915-MHz atmospheric pressure air MPT; and 4) the upper limit of the 915-MHz atmospheric pressure microwave plasma filament electron temperature increased from approximately 1 to approximately 3 eV as the absorbed power increased from 2.0 to 6.3 kW.