An approach to a non-LTE Saha equation based on the Druyvesteyn energy distribution function: a comparison between the electron temperature obtained from OES and the Langmuir probe analysis (original) (raw)
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Japanese Journal of Applied Physics, 2010
The effect of the electron energy distribution function (EEDF) on the population distribution of excited states is investigated in He and Ar plasmas sustained by a 2.45 GHz microwave at a discharge pressure of 1–5 Torr. The EEDF is measured with a Langmuir probe by Druyvesteyn's method and used as the input parameter of the collisional-radiative (CR) model calculation. The calculated population density of the excited states is compared with the results of optical emission spectroscopic measurement. Reasonable agreement is found between them. It is also confirmed that the measured EEDFs was depleted at energies above the first excitation potential of the discharge gas atoms. When we assume a Maxwellian EEDF and calculate the population distribution of excited states of the argon plasma, we find a marked discrepancy between the populations of excited states observed experimentally and those calculated by the CR model, while a discrepancy for the helium plasma is also found but is ...
On the kinetic and thermodynamic electron temperatures in non-thermal plasmas
EPL (Europhysics Letters), 2014
The framework to describe the out of equilibrium free electrons in cold plasmas is developed assuming the electron entropy is defined through the Boltzmann H-theorem. Our theory explains why the Saha-Boltzmann relation among higher-lying excited states by means of the electron kinetic temperature is fulfilled, even when free electrons are far from equilibrium. The thermodynamic electron temperature, pressure and chemical potential have been introduced through the derivatives of the electron entropy. It is demonstrated that under usual conditions in cold plasmas, e.g. when the electron distribution function possesses the Maxwellian, Druyvestein or Kappa functional forms, kinetic and thermodynamic electron temperatures yield same value.
Probe diagnostics of non‐Maxwellian plasmas
Journal of applied …, 1993
Various probe diagnostic methods have been applied to rf plasmas with non-Maxwellian electron energy distribution functions (EEDF) and the results of these diagnostic methods have been compared. Plasma density and electron temperature were obtained using standard procedures from the electron retardation region (classic Langmuir method), the ion saturation region, and the electron saturation region of the measured probe I/V characteristic. Measurements were made in a 13.56-MHz capacitive argon rf discharge at two gas pressures: p=O.O3 Torr, where stochastic electron heating is dominant, andp=0.3 Torr, where collisional electron heating dominates. Thus, the measured EEDF at each gas pressure manifests a distinct departure from thermodynamic equilibrium being bi-Maxwellian at 0.03 Torr and Druyvesteyn-like at 0.3 Torr. Considerable differences in electron density and temperature were obtained from the different parts of the probe characteristic and these values differ dramatically in many cases from those found from integration of the measured EEDF's, thus demonstrating that using standard procedures in non-Maxwellian plasma can give misleading results.
Advances in Physics: X
This paper describes the use of Optical Emission Spectroscopy (OES) to measure electron densities and temperatures in nonequilibrium plasmas. The ways to interpret relative lineintensities of neutral argon atoms are evaluated based upon a collisional-radiative model including atomic collisional processes. A conversion from an excitation temperature determined from relative line intensities assuming a Boltzmann population distribution to the thermal electron temperature in the electron temperature range 1-4 eV and electron density range 10 10-10 12 cm-3 is given. Procedures to obtain electron temperature T e and density N e of non-equilibrium argon plasma by OES measurement with collisional radiative model.
Journal of Applied Physics, 2006
The measurement of the electron mean kinetic energy by identifying the electron temperature and the excitation temperature obtained by optical emission spectroscopy is theoretically studied for two temperature argon plasmas at atmospheric pressure. Using a 32-level collisional radiative model in which both electron impact and argon-impact inelastic collisions are taken into account, it has been found that under certain conditions the argon inelastic collisions may cause a decrease of the argon excitation temperature so that the relation T e Ͼ T exc Ͼ T 0 is satisfied. This inequality also appears when electron losses due to diffusion are important and the electron density is lower than its equilibrium value.
Determination of the electron density in current-less argon plasma using Langmuir probe measurements
Vacuum, 2004
Langmuir probe measurements were performed in a specially designed D.C. discharge tube with coaxial electrodes in argon current-less plasma (gas pressure 60-130 Pa, discharge current 80 mA). It is well known, that the Langmuir probe yields reliable and easy to interpret results only in the case of low gas pressure. In the case of relatively high pressure, when one cannot neglect the finite probe radius and the effects of collisions in the probe sheath, the probe data used to determine the electron energy distribution function (EEDF) are distorted. In this report, we present the results produced by a computer code that solves the integral equation connecting the experimental second derivative data at relatively high pressure with the real EEDF. r
2004
A set of twenty four plasma glow discharge experiments using radio-frequency electromagnetic fields were carried out. The discharge pressure was 27 Pa. Dried air was used as the discharge gas. Axial radio-frequency fields between 0.6-1.2 MHz were applied. Four different values of the RF field intensity were used. For each case, the plasma Langmuir probe characteristics were measured. A computational method was used to extract the electron energy distribution function in each case. Values of the plasma density and plasma temperature were obtained directly from the fits. They compare well with values obtained using the conventional logarithmic method. The Maxwellian behaviour of the distribution function was established to hold in many but not in all cases. PACS numbers: 52.25.-b, 51.30.+i UDC 531.742
The European Physical Journal D, 2009
Experimental studies of the electron energy distribution function "EEDF" under well defined conditions in flowing afterglow plasma, using a Langmuir probe are reported. The EEDF is measured in He + 2 and Ar + dominated plasmas and in XeH + and XeD + dominated recombining plasmas. He is used as a buffer gas at medium pressures in all experiments (1600 Pa, 250 K). The deviation of the measured EEDF from Maxwellian distribution is shown to depend on plasma composition and on the processes governing the plasma decay. The influence of energetic electrons produced during the plasma decay on the body and tail of the EEDF is observed. The mechanism of energy balance in afterglow plasma is discussed.
Determination of electron temperature in neon RF discharge bymeans of collisional-radiative model
2007
A collisional-radiative model was used to determine the electron temperature in capacitively coupled RF (13.56 MHz) discharge in neon. Two discharge regimes at different pressures were investigated. The temperature was determined from the fit of the theoretical spectra to the spectra measured by optical emission spectroscopy. Three kinds of electron distribution function - Maxwellian, Bi-Maxwellian and Pseudo-Bi-Maxwellian - were considered. The results were compared with Particle-in-Cell/ Monte-Carlo simulation. The comparison of the fitted calculated and measured spectra shows a good agreement between the theory and experiment. The electron temperature, which was estimated from the fits, was approx. 6 eV in the sheath at neon pressure of 10 Pa and approx. 2 eV in the bulk plasma at neon pressure of 80 Pa.
On the Electron Temperature Measurements in a Medium Electron Density Plasmas
This paper reports the results of the spectroscopic electron temperature (Te) measurements in plasmas with electron densities ranging (0.3 -1.4)·10 17 cm -3 . The results of Te measurements obtained from various spectroscopic methods are mutually compared and discussed in relation to the condition for partial local thermodynamic equilibrium (PLTE). For the cases when the application of the spectroscopic techniques for Te measurements can not be justified on the bases of PLTE criterion, new method for determination of plasma electron temperature is proposed and tested.