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Title: Response of the plasma to the size of an anode electrode biased near the plasma potential

As the size of a positively biased electrode increases, the nature of the interface formed between the electrode and the host plasma undergoes a transition from an electron-rich structure (electron sheath) to an intermediate structure containing both ion and electron rich regions (double layer) and ultimately forms an electron-depleted structure (ion sheath). In this study, measurements are performed to further test how the size of an electron-collecting electrode impacts the plasma discharge the electrode is immersed in. This is accomplished using a segmented disk electrode in which individual segments are individually biased to change the effective surface area of the anode. Measurements of bulk plasma parameters such as the collected current density, plasma potential, electron density, electron temperature and optical emission are made as both the size and the bias placed on the electrode are varied. Abrupt transitions in the plasma parameters resulting from changing the electrode surface area are identified in both argon and helium discharges and are compared to the interface transitions predicted by global current balance [S. D. Baalrud, N. Hershkowitz, and B. Longmier, Phys. Plasmas 14, 042109 (2007)]. While the size-dependent transitions in argon agree, the size-dependent transitions observed in helium systematically occur at lower electrodemore » sizes than those nominally derived from prediction. Thus, the discrepancy in helium is anticipated to be caused by the finite size of the interface that increases the effective area offered to the plasma for electron loss to the electrode.« less
Authors:
 [1] ;  [1] ;  [2]
  1. Sandia National Laboratories (SNL-NM), Albuquerque, NM (United States)
  2. Univ. of Iowa, Iowa City, IA (United States). Dept. of Physics and Astronomy
Publication Date:
Report Number(s):
SAND2014-17544J
Journal ID: ISSN 1070-664X; PHPAEN; 537502; TRN: US1802973
Grant/Contract Number:
AC04-94AL85000; AC04-94SL85000
Type:
Accepted Manuscript
Journal Name:
Physics of Plasmas
Additional Journal Information:
Journal Volume: 21; Journal Issue: 10; Journal ID: ISSN 1070-664X
Publisher:
American Institute of Physics (AIP)
Research Org:
Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)
Sponsoring Org:
USDOE Office of Science (SC), Fusion Energy Sciences (FES) (SC-24)
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; 47 OTHER INSTRUMENTATION; Interfaces; Surface and interface chemistry; Ionospheric physics; Optical metrology; Ionospheric dynamics; Magnetospheric dynamics; Plasma interactions; Electrodes; Current density; Classical electromagnetism
OSTI Identifier:
1426895
Alternate Identifier(s):
OSTI ID: 1223593

Barnat, E. V., Laity, G. R., and Baalrud, S. D.. Response of the plasma to the size of an anode electrode biased near the plasma potential. United States: N. p., Web. doi:10.1063/1.4897927.
Barnat, E. V., Laity, G. R., & Baalrud, S. D.. Response of the plasma to the size of an anode electrode biased near the plasma potential. United States. doi:10.1063/1.4897927.
Barnat, E. V., Laity, G. R., and Baalrud, S. D.. 2014. "Response of the plasma to the size of an anode electrode biased near the plasma potential". United States. doi:10.1063/1.4897927. https://www.osti.gov/servlets/purl/1426895.
@article{osti_1426895,
title = {Response of the plasma to the size of an anode electrode biased near the plasma potential},
author = {Barnat, E. V. and Laity, G. R. and Baalrud, S. D.},
abstractNote = {As the size of a positively biased electrode increases, the nature of the interface formed between the electrode and the host plasma undergoes a transition from an electron-rich structure (electron sheath) to an intermediate structure containing both ion and electron rich regions (double layer) and ultimately forms an electron-depleted structure (ion sheath). In this study, measurements are performed to further test how the size of an electron-collecting electrode impacts the plasma discharge the electrode is immersed in. This is accomplished using a segmented disk electrode in which individual segments are individually biased to change the effective surface area of the anode. Measurements of bulk plasma parameters such as the collected current density, plasma potential, electron density, electron temperature and optical emission are made as both the size and the bias placed on the electrode are varied. Abrupt transitions in the plasma parameters resulting from changing the electrode surface area are identified in both argon and helium discharges and are compared to the interface transitions predicted by global current balance [S. D. Baalrud, N. Hershkowitz, and B. Longmier, Phys. Plasmas 14, 042109 (2007)]. While the size-dependent transitions in argon agree, the size-dependent transitions observed in helium systematically occur at lower electrode sizes than those nominally derived from prediction. Thus, the discrepancy in helium is anticipated to be caused by the finite size of the interface that increases the effective area offered to the plasma for electron loss to the electrode.},
doi = {10.1063/1.4897927},
journal = {Physics of Plasmas},
number = 10,
volume = 21,
place = {United States},
year = {2014},
month = {10}
}