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/H 2 flow rate of 40/0 to 40/8 L/min and current intensity variation from 500 to 700 A. The electron temperature (T e ) was determined based on the calculation of the relative intensity of two spectral lines, H a and H b . It was found that T e 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 H 2 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 T e when different powder sizes were injected. Correspondingly, electron densities ranged from 0.76 3 10 14 to 1.41 3 10 15 cm 23 and were obtained using Stark-effect broadening of the H b (486 nm) line under the assumption of local thermodynamic equilibrium (LTE).

How Hydrogen Admixture Changes Plasma Jet Characteristics in Spray Processes at Low Pressure

“…Figure 12 gives the radial profiles of the electron densities at spray distances of 500 mm and 800 mm for three different hydrogen admixtures to the plasma gas. They are of typical magnitude for expanding plasmas at low pressure [31,55] and suggest low ionization degrees of just a few percent. Electron densities were not determined where non-equilibrium must be assumed at the jet rims, as explained before.…”

Effects of the nozzle design on the properties of plasma jet and formation of YSZ coatings under low pressure conditions

“…The hydrogen atom is easily excited, so the electron temperature in the plasma jet was often calculated by the ratio of the two hydrogen spectral lines [19] . But in this experiment, the intensity of the H  (656.7 nm) spectrum is saturated.…”

Plasma Spray-PVD: Plasma Characteristics and Impact on Coating Properties

“…Electron densities and heavy particle temperatures were calculated by peak broadening analysis. Some initial results based on the first two hydrogen spectral lines of the Balmer series H α and H β obtained at VLPPS conditions are given in [6,7]. As the plasma jets are optically thin, the measurement is spatially integrated along the line of sight of the optical sampling setup [8].…”