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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. 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] ;  [2]
  1. Sandia National Laboratories, Albuquerque, New Mexico 87185 (United States)
  2. Department of Physics and Astronomy, University of Iowa, Iowa City, Iowa 52242 (United States)
Publication Date:
OSTI Identifier:
22299724
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physics of Plasmas; Journal Volume: 21; Journal Issue: 10; Other Information: (c) 2014 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; ANODES; ARGON; COMPARATIVE EVALUATIONS; CURRENT DENSITY; ELECTRON DENSITY; ELECTRON LOSS; ELECTRON TEMPERATURE; ELECTRONS; INTERMEDIATE STRUCTURE; PLASMA; PLASMA POTENTIAL; SURFACE AREA