A collisional-radiative model with an extended region of applicability is developed for an argon atom plasma. Atom-atom inelastic collisions and diffusion losses of the metastable states along with the electron-atom inelastic collisions and radiative processes are considered in this model, taking into account 65 effective levels. Among the analytical expressions used for the corresponding cross sections, special attention is paid to those determining the set of cross sections for excitation by electrons from the ground state, owing to the possibility of utilising the formulae recommended in kinetic modelling studies of discharges in argon or in mixtures including argon atoms. The numerical method developed makes it possible to investigate the mechanisms by which the excited levels are populated in a non-equilibrium argon plasma characterised (even in the case of a non-Maxwellian electron distribution) by a set of parameters, such as the electron kinetic temperature Te, the atom temperature Ta, the ion temperature Ti, the electron number density ne, the ground state atom population n1, the discharge tube (or the plasma column) radius R and the optical escape factors Lambda mn and Lambda m, which are dependent only on the quantities Ta, n1 and R in many cases of practical interest.

https://iopscience.iop.org/article/10.1088/0022-3727/22/5/009/pdf

A collisional-radiative model applicable to argon discharges over a wide range of conditions. I. Formulation and basic data

A magnetogasdynamic arc model due to Kovitya and Lowke has been combined with a collisional-radiative model of the argon atom to show how intense radiation from an arc can produce excited-state densities in the boundary of the arc which are far in excess of the densities corresponding to thermodynamic equilibrium Quantitative predictions based on this model have been compared with measurements recently reported by Farmer and Haddad There are encouraging similarities between theory and experiment, although it is suggested that the theory could be further improved by including the effect of resonance radiation which is scattered in the arc boundary

Departures from equilibrium in a free-burning argon arc

A microplasma suitable for material processing at atmospheric pressure in argon and argon-oxygen mixtures is being studied here. The microplasma is ignited by a high voltage dc pulse and sustained by low power (1–5W) at 450MHz. the mechanisms responsible for sustaining the microplasma require a more detailed analysis, which will be the subject of further study. Here it is shown that the microplasma is in nonequilibrium and appears to be in glow mode. The effect of power and oxygen content is also analyzed in terms of gas temperature and electron temperature. Both the gas temperature and the electron temperature have been determined by spectral emission and for the latter a very simple method has been used based on a collisional-radiative model. It is observed that power coupling is affected by a combination of factors and that prediction and control of the energy flow are not always straightforward even for simple argon plasmas. Varying gas content concentration has shown that oxygen creates a preferentia...

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Gas temperature and electron temperature measurements by emission spectroscopy for an atmospheric microplasma

A simple model and method is proposed here to determine argon metastable number densities and electron temperature with the assumption of a Maxwell-Boltzmann electron energy distribution. This method is based on the availability of experimental relative emission intensities of only four argon lines that originate from any of the 4p argon levels. The proposed model has a relatively wide range of validity for laboratory plasmas that contain argon gas and can be a valuable tool for the emerging field of atmospheric microplasmas, for which diagnostics is still limited. © 2006 American Institute of Physics. DOI: 10.1063/1.2390631 Plasmas are finding interest in a large number of applications and are becoming increasingly exploitable in already established plasma fields such as in material processing. This trend in plasma science is mainly due to a greater knowledge of the behavior of laboratory and technological plasmas. Diagnostic techniques play a major role in understanding plasmas and can help predicting the potential of plasmas when used for future applications. In particular, emission spectroscopy has revealed extremely useful insights when supported by very simple computational techniques. 1‐7 One of the advantages of emission spectroscopy is undoubtedly the noninvasive character; the practicality and the availability of low cost spectroscopy equipment have also been an incitement to the use of this diagnostic technique.

Method to determine argon metastable number density and plasma electron temperature from spectral emission originating from four 4p argon levels

A collisional-radiative (C-R) model is used to obtain the population number densities of the excited levels of neutral and singly charged ions in argon for 6000K<Tc<13000K for P=1 atm; radiative processes, atomic and electronic collisions altogether with diffusive phenomena are taken into consideration. The threshold value neth for the electronic density, corresponding to a Saha equilibrium for the lower-lying excited levels, is determined for each Te value. A simplified model allows evaluation of the influence of each process on the density of the set of metastable and pseudo-metastable atomic excited levels of the 3p5 4s electronic configuration. For the different zones of the discharge, the Saha and Boltzmann temperatures, which can be experimentally obtained, are compared to the electronic temperature Tc.

http://iopscience.iop.org/article/10.1088/0022-3727/16/3/019/pdf

Criteria for partial LTE in an argon thermal discharge at atmospheric pressure; validity of the spectroscopically measured electronic temperature

A collisional radiative model is used to obtain the number densities of the ground level and of the excited levels of neutral argon as a function of the local ne and Te values This model is first applied to a homogeneous and stationary medium for 5000K<Te<12000K The local values of the density of atoms in the ground level and of the heavy particles (neutrals and ions) temperature Tg in a non-LTE discharge are determined The C-R model is then applied to the positive column of a stationary argon arc The ambipolar flux of electrons is evaluated and compared to the net rate of electron production

https://iopscience.iop.org/article/10.1088/0022-3727/11/16/006/pdf

J Bacri

Papers

Influence of atom-atom collisions on thermal equilibrium in argon arc discharges at atmospheric pressure