Emission spectroscopic study of a low pressure supersonic Ar-H2 DC plasma jet

Abstract

An emission spectroscopic study is reported of the temperature and the electron density distributions in a DC plasma jet at atmospheric and low pressure conditions. A standard DC plasma spraying torch is used with an Ar-H2 mixture as the plasma gas (17% H2 by volume) at a power level of 30 kW (current=600 A, voltage=50 V). Results were obtained for chamber pressures of 100 kPa, 52 kPa and 20 kPa. Electron density measurements were carried out by the Stark broadening of the Hbeta line and from the continuum recombination of the Ar+ and H+ ions. The temperature is obtained by using a Boltzmann plot of the neutral argon lines and the absolute intensity measurements of the argon lines. The results confirm that local thermodynamic equilibrium (LTE) conditions prevail throughout most of the temperature field at pressures of 100 and 53 kPa. Important deviations from LTE conditions are noted at a chamber pressure of 20 kPa. The results at the lowest pressure condition (20 kPa) show important axial variations of the electron density which coincide with the observed diamond shock wave in the plasma jet.