Electron Temperature and Density of the Plasma Measured by Optical Emission Spectroscopy in VLPPS Conditions

Abstract

Measurements of electron temperature and electron density have been carried out on a plasma plume under very low pressure conditions (P = 1 mbar) using optical emission spectroscopy. The plasma torch was operated at a power level of 20-55 kW corresponding to an Ar/H2 flow rate of 40/0 to 40/8 L/min and current intensity variation from 500 to 700 A. The electron temperature (Te) was determined based on the calculation of the relative intensity of two spectral lines, Hα and Hβ. It was found that Te decreased from 0.2 to 0.9 eV with increasing detection distance from the nozzle exit from 40 to 60 cm. Changes in the current and the flow rate of H2 also had a significant impact on it. There are significant fluctuations in the hydrogen emission intensity when using current intensity of 700 A or with increasing hydrogen fraction in the mixture. However, it seemed that there was no evident change in Te when different powder sizes were injected. Correspondingly, electron densities ranged from 0.76 × 1014 to 1.41 × 1015 cm−3 and were obtained using Stark-effect broadening of the Hβ (486 nm) line under the assumption of local thermodynamic equilibrium (LTE).