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 (N ₂ -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 N ₂ -MIP, and an Fe solution was used to determine the excitation temperature distribution of the N ₂ -MIP, which was obtained by using a Boltzmann plot under the assumption of LTE. In addition, rotational temperature measurements were carried out using the N ₂ ⁺ (0–0):B ² Σ _u ⁺ →X ² Σ _g ⁺ band. Because the H _β line (486.13 nm) could not be excited in the N ₂ -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 N ₂ -MIP. The degree of ionization of various elements in the N ₂ -MIP was also calculated. The spatial characteristics of the N ₂ -MIP were compared with those of the Ar-ICP.