Thermal Temperature Measurements of Plasma Torch by Alexandrite Effect Spectropyrometer

An alexandrite effect spectropyrometer is used to directly measure the thermal temperature of an argon gas plasma jet from a 100？kW DC plasma torch, and the directly measured thermal temperature of the plasma is ？K. By using the spectral correction function to delete the spectral lines and to correct its underlying spectrum of the relative spectral power distribution of the plasma jet, the remaining continuum spectral power distribution represents the thermal spectral emission of the plasma jet. The calculated thermal temperature of the corrected relative continuum spectral power distribution by the spectropyrometer is 10106？K ？K, which is the true thermal temperature of the plasma jet. The blackbody level (BL) of the thermal plasma jet is defined as the ratio of the true thermal temperature to the directly measured temperature, and the blackbody level is a measure of how well the thermal plasma jet approaches a blackbody. The accuracy of directly measured thermal temperature depends on the blackbody level, the higher the blackbody level, and the higher the thermal temperature measurement accuracy. 1. Introduction Plasma jets generated in DC arc torches are used for spraying, cutting, synthesis, carbon material vaporization, and decomposition of persistent chemical substances. The temperature fluctuation of a plasma torch significantly reduces its reliability for industrial applications. The characteristics of emission spectra from the flame jet of a plasma torch directly indicate the plasma properties and operation conditions. It’s a well-established technique [1–3] to measure the kinetic temperature using optical emission spectroscopy (OES) methods; however, none of the methods were accurate under temporal and spatial changing conditions. Local Thermodynamic Equilibrium (LTE) is assumed for calculating the temperature from the populations of excited levels. The calculated temperature is based on the absolute and relative intensities of various atomic lines. The temperature is often calculated from the ratios of gas atomic to ionic line emission coefficients by the Saha equation using the measured electron number density or is calculated by the ratio of spectral lines by the Ornstein method. It assumes that collisions are predominant and the temperature and concentration gradients are low, which are not true in jet fringes or close to electrodes or substrates. The diffusion of particles and electrons plays an important role in the regions of the plasma. The temperatures calculated from the spectral lines are generally overestimated [4]. Planck’s