Nonthermal atmospheric rf plasma in onedimensional spherical coordinates: Asymmetric sheath structure and the discharge mechanism
Abstract
We present onedimensional simulations of atmospheric pressure rfexcited plasma with two concentric spherical electrodes and the inner electrode powered. The gas used is helium with 0.1% nitrogen addition. The gap distance between the inner and outer electrodes is 1 mm. The coupled continuity equations and electron energy equation are solved with Poisson's equation using the finite element method. A mode transition is observed in the discharge powervoltage curve between 1 and 1000 mW. In the low power mode, ionization rate peaks only near the inner electrode. The electronimpact excitation and ionization rates peak in the local cathodic phase. In the high power mode, the rate of ionization peaks near the outer electrode as well as the inner electrode. The inner sheath significantly shrinks and the direct electronimpact ionization is the primary ionization reaction near the inner electrode. The ionization rate near the outer electrode is due to Ohmic sheath oscillation heating of electrons, resulting in a peak in metastable helium creation. Penning ionization is the major ionization reaction near the outer electrode. Thus, two different ionization mechanisms coexist near the inner and outer electrodes. Electron heating near the outer electrode may have implications for surface processing in atmospheric pressure microdischarges.more »
 Authors:
 Department of Mechanical Engineering, University of Tokyo, Tokyo 1138656 (Japan)
 (United States)
 Publication Date:
 OSTI Identifier:
 20982789
 Resource Type:
 Journal Article
 Resource Relation:
 Journal Name: Journal of Applied Physics; Journal Volume: 101; Journal Issue: 7; Other Information: DOI: 10.1063/1.2715745; (c) 2007 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA)
 Country of Publication:
 United States
 Language:
 English
 Subject:
 70 PLASMA PHYSICS AND FUSION TECHNOLOGY; APPROXIMATIONS; ASYMMETRY; ATMOSPHERIC PRESSURE; CONTINUITY EQUATIONS; COORDINATES; ELECTRIC FIELDS; ELECTRIC POTENTIAL; ELECTRODES; ELECTRON DENSITY; ELECTRONS; EXCITATION; FINITE ELEMENT METHOD; HELIUM; HIGHFREQUENCY DISCHARGES; IONIZATION; NITROGEN ADDITIONS; PLASMA; PLASMA SHEATH; PLASMA SIMULATION; POISSON EQUATION
Citation Formats
Sakiyama, Yukinori, Graves, David B., and Department of Chemical Engineering, University of California, Berkeley, California 94720. Nonthermal atmospheric rf plasma in onedimensional spherical coordinates: Asymmetric sheath structure and the discharge mechanism. United States: N. p., 2007.
Web. doi:10.1063/1.2715745.
Sakiyama, Yukinori, Graves, David B., & Department of Chemical Engineering, University of California, Berkeley, California 94720. Nonthermal atmospheric rf plasma in onedimensional spherical coordinates: Asymmetric sheath structure and the discharge mechanism. United States. doi:10.1063/1.2715745.
Sakiyama, Yukinori, Graves, David B., and Department of Chemical Engineering, University of California, Berkeley, California 94720. Sun .
"Nonthermal atmospheric rf plasma in onedimensional spherical coordinates: Asymmetric sheath structure and the discharge mechanism". United States.
doi:10.1063/1.2715745.
@article{osti_20982789,
title = {Nonthermal atmospheric rf plasma in onedimensional spherical coordinates: Asymmetric sheath structure and the discharge mechanism},
author = {Sakiyama, Yukinori and Graves, David B. and Department of Chemical Engineering, University of California, Berkeley, California 94720},
abstractNote = {We present onedimensional simulations of atmospheric pressure rfexcited plasma with two concentric spherical electrodes and the inner electrode powered. The gas used is helium with 0.1% nitrogen addition. The gap distance between the inner and outer electrodes is 1 mm. The coupled continuity equations and electron energy equation are solved with Poisson's equation using the finite element method. A mode transition is observed in the discharge powervoltage curve between 1 and 1000 mW. In the low power mode, ionization rate peaks only near the inner electrode. The electronimpact excitation and ionization rates peak in the local cathodic phase. In the high power mode, the rate of ionization peaks near the outer electrode as well as the inner electrode. The inner sheath significantly shrinks and the direct electronimpact ionization is the primary ionization reaction near the inner electrode. The ionization rate near the outer electrode is due to Ohmic sheath oscillation heating of electrons, resulting in a peak in metastable helium creation. Penning ionization is the major ionization reaction near the outer electrode. Thus, two different ionization mechanisms coexist near the inner and outer electrodes. Electron heating near the outer electrode may have implications for surface processing in atmospheric pressure microdischarges. The local field approximation (LFA) in high power mode fails to predict the ionization rate peak near the outer electrode due to its inability to properly account for electron diffusion in the presence of both a strong electric field and electron density gradient. However, use of the LFA is adequate to model the low power mode and it correctly predicts the existence of the mode transition.},
doi = {10.1063/1.2715745},
journal = {Journal of Applied Physics},
number = 7,
volume = 101,
place = {United States},
year = {Sun Apr 01 00:00:00 EDT 2007},
month = {Sun Apr 01 00:00:00 EDT 2007}
}

The keynote of our research is to study the gas phase chemistry in an atmospheric pressure Ar/NH{sub 3} cylindrical dielectric barrier discharge, which is very important to produce the ironnitride magnetic fluid. For this purpose, a homemade one dimensional fluid model with the ScharfetterGummel method has been developed. The equations solved are the particle balances, assuming a driftdiffusion approximation for the fluxes, and the electron energy equation. The selfconsistent electric field is obtained by the simultaneous solution of Poisson's equation. The simulations were carried out for the different ammonia concentrations (2%, 3.5%, and 7%), at a voltage of 1 kV,more »

Spherical shell model of an asymmetric rf discharge
A spherical shell model is used to study ion transport and bias voltage formation in asymmetric, capacitive rf discharges, which have unequal areas A and glowtoelectrode voltages V at the powered (a) and grounded (b) electrodes. Ions are generated by thermal electron ionization and are lost by ambipolar diffusion in the glow. Resonant charge transfer with a constant cross section is assumed to dominate the ion transport. We obtain the density ratio scaling n/sub a//n/sub b/proportional(A/sub b//A/sub a/ )/sup 7//sup ///sup 24/, where n is the density at the glowsheath edge. Three electrode sheath models are considered: collisionless ions, collisionalmore » 
Dynamic model of the radiofrequency plasma sheath in a highly asymmetric discharge cell
A selfconsistent fluid model for the radiofrequency sheath at the powered electrode of a highly asymmetric discharge cell is developed and solved. The model assumes timeindependent ion motion and inertialess electrons. The voltage on the powered electrode, assumed to be sinusoidal, is shared between the powered sheath and a series resistance that represents the remainder of the discharge. The model includes ion collisions, sheath conduction currents, and secondary electron emission from the electrode surface. Model results are compared with previous sheath models and with experiment. Current wave forms predicted by the model closely resemble the nonsinusoidal current wave forms measuredmore » 
An Angular Leakage Correction for Modeling a Hemisphere, Using OneDimensional Spherical Coordinates
A radially dependent, angular leakage correction was applied to a onedimensional, multigroup neutron diffusion theory computer code to accurately model hemispherical geometry. This method allows the analyst to model hemispherical geometry, important in nuclear criticality safety analyses, with onedimensional computer codes, which execute very quickly. Rapid turnaround times for scoping studies thus may be realized. This method uses an approach analogous to an axial leakage correction in a onedimensional cylinder calculation. The twodimensional Laplace operator was preserved in spherical geometry using a leakage correction proportional to 1/r{sup 2}, which was folded into the onedimensional spherical calculation on a meshbymesh basis.more »