Axial variation of electron number density in thermal plasma spray jets

Abstract.

The electron number density has been measured in a plasma spray torch using Stark broadening of H$_{\beta}$ and Ar-I (430 nm) line. A small amount of hydrogen (1% by volume in argon gas) was introduced to study the H$_{\beta}$ line profile. Axial variation of electron number density has been determined up to a distance of 20 mm from the nozzle exit point of spray torch. The plasma torch was operated at 5 and 10 kW power level and flow of argon was kept at 25 liters per minute. Using the measured excitation temperature data under same experimental conditions, the electron number density has also been calculated using Saha equation. Comparison of electron number densities measured from Stark broadening with those derived from excitation temperature measurements under the assumption of local thermodynamic equilibrium (LTE) in thermal plasma jets indicate about the deviation from LTE in thermal plasma jets. The electron number density measurement using Stark broadening of Ar-I (430 nm) line will be particularly useful when only argon gas is used in thermal plasma jets.