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15 Feb 2003

Volume 93, Issue 4, pp. 1859-2309

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Determination of gas temperature in an open-air atmospheric pressure plasma torch from resolved plasma emission

James M. Williamson and Charles A. DeJoseph

J. Appl. Phys. 93, 1893 (2003); http://dx.doi.org/10.1063/1.1536736 (6 pages) | Cited 10 times

Online Publication Date: 30 January 2003

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The resolved emission spectrum of an open-air atmospheric pressure plasma torch was recorded with a 0.5 m spectrometer and CCD camera. The plasma emission under these conditions was found to be dominated by continuum radiation and emission from species, which obscured large portions of the N2 second positive emission spectrum. Despite these difficulties, the gas temperature of the torch could be determined from a fit of partially resolved N2+ first negative vibrational transitions and a blackbody fit to the continuum radiation. The vibrational temperature, determined from a Boltzmann plot, was 4300±900 K while the blackbody radiation temperature was 4400±400 K. To check these gas temperature determinations, measured spectra over selected spectral regions were compared with spectral simulations using N2+ first negative emission, N2 second positive emission, and a blackbody. Best agreement between measured and simulated spectra was with blackbody temperature, rotational temperature, and vibrational temperature set to 4400 K. © 2003 American Institute of Physics.
Show PACS
52.75.Hn Plasma torches
52.70.Kz Optical (ultraviolet, visible, infrared) measurements
52.25.Os Emission, absorption, and scattering of electromagnetic radiation

Ion energy distribution functions of vacuum arc plasmas

Eungsun Byon and André Anders

J. Appl. Phys. 93, 1899 (2003); http://dx.doi.org/10.1063/1.1539535 (8 pages) | Cited 31 times

Online Publication Date: 30 January 2003

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The velocity distribution function of vacuum arc ions can be measured by a time-of-flight technique. The measuring principle makes use of the well-justified assumption that the ion drift velocity from the cathode spot region to a collector is approximately constant. It is shown that the negative time derivative of the collector current is directly proportional to the ion distribution function provided that the time-averaged emission of ions from cathode spots is constant until the arc is rapidly switched off. In the experiment, arc termination took about 700 ns, which is much faster than the decay of the ion current measured at the collector placed more than 2 m from the cathode. The experimental distribution functions for most cathode materials show one large peak with a tail and one or more small peaks at higher ion velocities. The typical peak position is at about 104 m/s, with the precise values being material specific. The distribution functions for some materials exhibit not one but several peaks. No conclusive answer can be given about the nature of these peaks. Arguments are presented that the peaks are not caused by different charge states or plasma contamination but rather are due to insufficiently averaged source fluctuations and/or acceleration by plasma instabilities. © 2003 American Institute of Physics.
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52.80.Vp Discharge in vacuum
52.80.Mg Arcs; sparks; lightning; atmospheric electricity
52.25.Dg Plasma kinetic equations
52.70.Nc Particle measurements
52.25.Fi Transport properties
52.35.Qz Microinstabilities (ion-acoustic, two-stream, loss-cone, beam-plasma, drift, ion- or electron-cyclotron, etc.)

Characterization of neutral, positive, and negative species in a chlorine high-density surface-wave plasma

L. Stafford, J. Margot, M. Chaker, and O. Pauna

J. Appl. Phys. 93, 1907 (2003); http://dx.doi.org/10.1063/1.1538313 (7 pages) | Cited 10 times

Online Publication Date: 30 January 2003

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This article reports an experimental study of the influence of the plasma parameters on the concentration of neutral and ion species in a chlorine high-density plasma sustained by surface waves. The investigation focuses on the dependence of the concentrations of Cl, Cl2, Cl+, Cl2+, Cl−, and electrons on the gas pressure in the 0.1 to 10 mTorr range, and on the intensity of a confinement magnetic field. The results show that a high dissociation degree (up to 90%) can be achieved even with a very modest power level (250 W, power density of about 2 mW/cm3), provided the pressure is low enough (i.e., less than 1 mTorr). It was also found that Cl+ is the main positive ion and that electrons are the main negative charge carrier at lower pressure. When the gas pressure is higher than a few mTorr, Cl2+ becomes dominant with Cl− as the negative charge carrier. The behavior of the positive ion and neutral species concentrations is compared to the results of a simple model based on creation–losses rate equations for the various species. It is shown that for a given magnetic field intensity, there is a critical pressure above which diffusion can be neglected in comparison with ion–ion recombination and charge transfer. © 2003 American Institute of Physics.
Show PACS
52.25.Kn Thermodynamics of plasmas
52.70.-m Plasma diagnostic techniques and instrumentation
52.35.-g Waves, oscillations, and instabilities in plasmas and intense beams
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