Characterization of a Microwave-Induced Atmospheric-Pressure Ar–N2 Plasma Pencil

A microwave-induced atmospheric-pressure plasma pencil was developed with an Ar-N
₂
gas mixture supplied to a coaxial transmission line. High-frequency simulation showed sufficient high electric field at the tip of the inner conductor, which resulted to automatic plasma ignition and a stable operation. The dependence of the characteristics of the plasma pencil from Ar and N
₂
gas flow rates was extensively studied. At moderate Ar gas flow rates, the plasma pencil can be operated at several tens of watts to achieve a near room-temperature and centimeter-long Ar-N
₂
plasma plume with OH and NO radicals as active species. Optical emission spectroscopy was also used to determine the vibrational and rotational temperatures of the plasma pencil. The vibrational temperature of N
₂
from the second positive system (2PS) can be obtained at moderate gas flow rates, since there was a good linear fitting with the Boltzmann distribution. At these gas flow rates, the vibrational and rotational temperatures of N
₂
from 2PS were found to be 0.42 and 0.29 eV, respectively.