Computational technique for plasma parameters determination using Langmuir probe data
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SMA DIAGNOSTICS
Computational Technique for Plasma Parameters Determination Using Langmuir Probe Data1 C. Negreaa, b, V. Maneaa, V. Covleaa, and A. Jipaa a
Faculty of Physics, University of Bucharest, P.O. Box MG11, RO0771253 Bucharest–Magurele, Romania b Institute of Space Science, P.O. Box MG23, RO077125, Bucharest–Magurele, Romania Received July 22, 2010; in final form, November 11, 2010
Abstract—In the present work, we consider a new numerical method for processing the experimental infor mation on the electron energy distribution function obtained with a Langmuir probe in a lowpressure plasma. This method offers the possibility to establish the temperature and concentration of the electrons for different forms of the distribution function. Some specific difficulties of the previous methods used to do such estimations are surpassed using the method proposed in this work. DOI: 10.1134/S1063780X11050096 1
1. INTRODUCTION
Research and development for new materials and their manufacturing have been accelerating during the last years. Processing by plasma assisted techniques is used in various areas of production and manufacturing [1, 2]. The plasma state covers an energy range spanning several orders of magnitude, more than the other phases together. In length scales it extends from nanometers to kiloparsecs (1 parsec = 3.26 light years). In the plasma, a large number of variables affect the balance between the competing chemical and physical processes. Appropriate reliable diagnostic techniques are necessary to provide an understanding of the plasma types and of the phenomena taking place [3, 4]. Electrostatic probes are indispensable diagnostic tools for lowpressure plasmas. In such plasmas the electrons are not at energetic equilibrium with ions or neutrals, having a much greater temperature, Te, than the temperature of the ions, Ti, and of the neutrals, Tn. Although the most common theoretical approach starts with the presumption that the energy distribu tion function is a Maxwellian one, both for electrons and ions, in lowpressure plasmas the electron energy distribution function (EEDF) for electrons is usually a nonMaxwellian one and the electron temperature has to be regarded as the effective value (Teff) correspond ing to the mean electron energy computed from EEDF [5–7]. The purpose of this paper is to present a particular computational technique for calculating the EEDF from the currentvoltage characteristic of a Langmuir probe. The experimental distribution is compared to 1 The article is published in the original.
the Maxwell and Druyvesteyn theoretical distribu tions. The electron density and temperatures that pro vide the best fit to the experimental data are specified for both distributions. The method is particularly important in the case of plasmas which contain more than one electronic population (from the viewpoint of the energy distribution). The computational tech nique includes a smoothing procedure for the elimina tion of the statistical fluctuations of the experimental da
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