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Title: Theory and simulation of anode spots in low pressure plasmas

Abstract

When electrodes are biased above the plasma potential, electrons accelerated through the associated electron sheath can dramatically increase the ionization rate of neutrals near the electrode surface. It has previously been observed that if the ionization rate is great enough, a double layer separates a luminous high-potential plasma attached to the electrode surface (called an anode spot or fireball) from the bulk plasma. Here, results of the first 2D particle-in-cell simulations of anode spot formation are presented along with a theoretical model describing the formation process. It is found that ionization leads to the build-up of an ion-rich layer adjacent to the electrode, forming a narrow potential well near the electrode surface that traps electrons born from ionization. It is shown that anode spot onset occurs when a quasineutral region is established in the potential well and the density in this region becomes large enough to violate the steady-state Langmuir condition, which is a balance between electron and ion fluxes across the double layer. A model for steady-state properties of the anode spot is also presented, which predicts values for the anode spot size, double layer potential drop, and form of the sheath at the electrode by considering particle, power,more » and current balance. Furthermore, these predictions are found to be consistent with the presented simulation and previous experiments.« less

Authors:
 [1];  [2];  [1];  [2];  [2]
  1. Univ. of Iowa, Iowa City, IA (United States)
  2. Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)
Publication Date:
Research Org.:
Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)
Sponsoring Org.:
USDOE National Nuclear Security Administration (NNSA)
OSTI Identifier:
1464203
Alternate Identifier(s):
OSTI ID: 1409873
Report Number(s):
SAND-2017-8476J
Journal ID: ISSN 1070-664X; 663066; TRN: US1902380
Grant/Contract Number:  
AC04-94AL85000; AC04-94SL85000; AC05-06OR23100
Resource Type:
Accepted Manuscript
Journal Name:
Physics of Plasmas
Additional Journal Information:
Journal Volume: 24; Journal Issue: 11; 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

Scheiner, Brett, Barnat, Edward V., Baalrud, Scott D., Hopkins, Matthew M., and Yee, Benjamin Tong. Theory and simulation of anode spots in low pressure plasmas. United States: N. p., 2017. Web. doi:10.1063/1.4999477.
Scheiner, Brett, Barnat, Edward V., Baalrud, Scott D., Hopkins, Matthew M., & Yee, Benjamin Tong. Theory and simulation of anode spots in low pressure plasmas. United States. doi:10.1063/1.4999477.
Scheiner, Brett, Barnat, Edward V., Baalrud, Scott D., Hopkins, Matthew M., and Yee, Benjamin Tong. Wed . "Theory and simulation of anode spots in low pressure plasmas". United States. doi:10.1063/1.4999477. https://www.osti.gov/servlets/purl/1464203.
@article{osti_1464203,
title = {Theory and simulation of anode spots in low pressure plasmas},
author = {Scheiner, Brett and Barnat, Edward V. and Baalrud, Scott D. and Hopkins, Matthew M. and Yee, Benjamin Tong},
abstractNote = {When electrodes are biased above the plasma potential, electrons accelerated through the associated electron sheath can dramatically increase the ionization rate of neutrals near the electrode surface. It has previously been observed that if the ionization rate is great enough, a double layer separates a luminous high-potential plasma attached to the electrode surface (called an anode spot or fireball) from the bulk plasma. Here, results of the first 2D particle-in-cell simulations of anode spot formation are presented along with a theoretical model describing the formation process. It is found that ionization leads to the build-up of an ion-rich layer adjacent to the electrode, forming a narrow potential well near the electrode surface that traps electrons born from ionization. It is shown that anode spot onset occurs when a quasineutral region is established in the potential well and the density in this region becomes large enough to violate the steady-state Langmuir condition, which is a balance between electron and ion fluxes across the double layer. A model for steady-state properties of the anode spot is also presented, which predicts values for the anode spot size, double layer potential drop, and form of the sheath at the electrode by considering particle, power, and current balance. Furthermore, these predictions are found to be consistent with the presented simulation and previous experiments.},
doi = {10.1063/1.4999477},
journal = {Physics of Plasmas},
number = 11,
volume = 24,
place = {United States},
year = {2017},
month = {11}
}

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