Spatial Characterization of Emission Intensities and Temperatures of a High Power Nitrogen Microwave-induced Plasma

Abstract

The spatial characterization of a high power nitrogen microwave-induced plasma (N₂-MIP), using an Okamoto cavity, was undertaken. The plasma operating conditions were fixed during all the experiments at a microwave frequency of 2.45 GHz, an incident power of 1.3 kW, a plasma gas flow rate of 11.0 l min^-1, a carrier gas flow rate of 1.0 l min^-1 and a sample uptake rate of 1.6 ml min^-1. A Ca solution was used to measure the emission intensity distribution for both Ca atom and ion lines in the N₂-MIP, and an Fe solution was used to determine the excitation temperature distribution of the N₂-MIP, which was obtained by using a Boltzmann plot under the assumption of LTE. In addition, rotational temperature measurements were carried out using the N₂⁺ (0–0):B²Σ_u ⁺→X²Σ_g⁺ band. Because the H_βline (486.13 nm) could not be excited in the N₂-MIP, measurement of the electron number density was carried out by a method involving the Saha equation using both the emission intensity ratio (Ca II:Ca I) and the excitation temperature of the N₂-MIP. The degree of ionization of various elements in the N₂-MIP was also calculated. The spatial characteristics of the N₂-MIP were compared with those of the Ar-ICP.

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