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Title: Investigation of the short argon arc with hot anode. I. Numerical simulations of non-equilibrium effects in the near-electrode regions

Abstract

The atmospheric pressure arcs have recently found application in the production of nanoparticles. The distinguishing features of such arcs are small length and hot ablating anode characterized by intensive electron emission and radiation from its surface. We performed a one-dimensional modeling of argon arc, which shows that near-electrode effects of thermal and ionization non-equilibrium play an important role in the operation of a short arc, because the non-equilibrium regions are up to several millimeters long and are comparable to the arc length. The near-anode region is typically longer than the near-cathode region and its length depends more strongly on the current density. The model was extensively verified and validated against previous simulation results and experimental data. The Volt-Ampere characteristic (VAC) of the near-anode region depends on the anode cooling mechanism. The anode voltage is negative. In the case of strong anode cooling (water-cooled anode) when the anode is cold, temperature and plasma density gradients increase with current density, resulting in a decrease of the anode voltage (the absolute value increases). Falling VAC of the near-anode region suggests the arc constriction near the anode. Without anode cooling, the anode temperature increases significantly with the current density, leading to a drastic increasemore » in the thermionic emission current from the anode. Correspondingly, the anode voltage increases to suppress the emission, and the opposite trend in the VAC is observed. Here, the results of simulations were found to be independent of sheath model used: collisional (fluid) or collisionless model gave the same plasma profiles for both near-anode and near-cathode regions.« less

Authors:
ORCiD logo [1]; ORCiD logo [1]; ORCiD logo [2];  [1]
  1. Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)
  2. Keiser Univ., Fort Lauderdale, FL (United States)
Publication Date:
Research Org.:
Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Fusion Energy Sciences (FES) (SC-24)
OSTI Identifier:
1419791
Alternate Identifier(s):
OSTI ID: 1417712
Grant/Contract Number:
AC02-09CH11466
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Physics of Plasmas
Additional Journal Information:
Journal Volume: 25; Journal Issue: 1; Journal ID: ISSN 1070-664X
Publisher:
American Institute of Physics (AIP)
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY

Citation Formats

Khrabry, A., Kaganovich, I. D., Nemchinsky, V., and Khodak, A.. Investigation of the short argon arc with hot anode. I. Numerical simulations of non-equilibrium effects in the near-electrode regions. United States: N. p., 2018. Web. doi:10.1063/1.5007082.
Khrabry, A., Kaganovich, I. D., Nemchinsky, V., & Khodak, A.. Investigation of the short argon arc with hot anode. I. Numerical simulations of non-equilibrium effects in the near-electrode regions. United States. doi:10.1063/1.5007082.
Khrabry, A., Kaganovich, I. D., Nemchinsky, V., and Khodak, A.. Mon . "Investigation of the short argon arc with hot anode. I. Numerical simulations of non-equilibrium effects in the near-electrode regions". United States. doi:10.1063/1.5007082.
@article{osti_1419791,
title = {Investigation of the short argon arc with hot anode. I. Numerical simulations of non-equilibrium effects in the near-electrode regions},
author = {Khrabry, A. and Kaganovich, I. D. and Nemchinsky, V. and Khodak, A.},
abstractNote = {The atmospheric pressure arcs have recently found application in the production of nanoparticles. The distinguishing features of such arcs are small length and hot ablating anode characterized by intensive electron emission and radiation from its surface. We performed a one-dimensional modeling of argon arc, which shows that near-electrode effects of thermal and ionization non-equilibrium play an important role in the operation of a short arc, because the non-equilibrium regions are up to several millimeters long and are comparable to the arc length. The near-anode region is typically longer than the near-cathode region and its length depends more strongly on the current density. The model was extensively verified and validated against previous simulation results and experimental data. The Volt-Ampere characteristic (VAC) of the near-anode region depends on the anode cooling mechanism. The anode voltage is negative. In the case of strong anode cooling (water-cooled anode) when the anode is cold, temperature and plasma density gradients increase with current density, resulting in a decrease of the anode voltage (the absolute value increases). Falling VAC of the near-anode region suggests the arc constriction near the anode. Without anode cooling, the anode temperature increases significantly with the current density, leading to a drastic increase in the thermionic emission current from the anode. Correspondingly, the anode voltage increases to suppress the emission, and the opposite trend in the VAC is observed. Here, the results of simulations were found to be independent of sheath model used: collisional (fluid) or collisionless model gave the same plasma profiles for both near-anode and near-cathode regions.},
doi = {10.1063/1.5007082},
journal = {Physics of Plasmas},
number = 1,
volume = 25,
place = {United States},
year = {Mon Jan 22 00:00:00 EST 2018},
month = {Mon Jan 22 00:00:00 EST 2018}
}

Journal Article:
Free Publicly Available Full Text
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  • A short atmospheric pressure argon arc is studied numerically and analytically. In a short arc with an inter-electrode gap of several millimeters, non-equilibrium effects in plasma play an important role in operation of the arc. High anode temperature leads to electron emission and intensive radiation from its surface. A complete, self-consistent analytical model of the whole arc comprising of models for near-electrode regions, arc column, and a model of heat transfer in cylindrical electrodes was developed. The model predicts the width of non-equilibrium layers and arc column, voltages and plasma profiles in these regions, and heat and ion fluxes tomore » the electrodes. Parametric studies of the arc have been performed for a range of the arc current densities, inter-electrode gap widths, and gas pressures. The model was validated against experimental data and verified by comparison with numerical solution. In conclusion, good agreement between the analytical model and simulations and reasonable agreement with experimental data were obtained.« less
    Cited by 1
  • A spectroscopic investigation was made of the anode plasma of a pulsed vacuum arc with an aluminum anode and a molybdenum cathode. The arc was triggered by a third trigger electrode and was driven by a 150-A 10-$mu$s current pulse. The average current density at the anode was sufficiently high that anode spots were formed; these spots are believed to be the source of the aluminum in the plasma investigated in this experiment. By simultaneously measuring spectral emission lines of Al I, Al II, and Al III, the plasma electron temperature was shown to decrease sequentially through the norm temperaturesmore » of Al III, Al II, and Al I as the arc was extinguished. The Boltzmann distribution temperature T/ subD/ of four Al III excited levels was shown to be kT/subD//e=2.0plus-or- minus0.5 V, and the peak Al III 4D excited state density was shown to be about 5times10$sup 17$ m$sup -3$. These data suggest a non-local-thermodynamic- equilibrium (non-LTE) model of the anode plasma when compared with the Al$sup 3+$ production in the plasma. The plasma was theoretically shown to be optically thin to the observed Al III spectral lines. (auth)« less
  • Experimental studies of a free-burning, high-intensity argon arc operated at 800 Torr with a solid, molten, or resolidified copper anode demonstrate that the cathode region is not affected by Cu vapor from the anode. Also Cu vapor concentrations in the arc core (beyond 1 mm from the anode surface) are negligible. In contrast, there is a strong effect of the Cu vapor on the anode region of the arc. The arc fringes become electrically conducting due to the presence of Cu vapor, resulting in a flattening of the current density distribution and a corresponding drop of the temperature in themore » arc core. At the same time, the overall arc voltage shows a slight drop (<1 V). In the case of the resolidified anode, the overall arc voltage increases, which seems to be associated with the distribution of the stagnation flow in front of the anode due to a dip in the center of the anode.« less