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Title: Instability, Collapse and Oscillation of Sheaths Caused by Secondary Electron Emission

Abstract

The Debye sheath is shown to be unstable under general conditions. For surface materials with sufficient secondary electron emission (SEE) yields, the surface's current-voltage characteristic has an unstable branch when the bulk plasma temperature (Te ) exceeds a critical value, or when there are fast electron populations present. The plasma-surface interaction becomes dynamic where the sheath may undergo spontaneous transitions or oscillations. Using particle-in-cell simulations, we analyze sheath instabilities occurring in a high Te plasma slab bounded by walls with SEE. As the plasma evolves, whenever the sheath enters an unstable state, its amplitude rapidly collapses, allowing a large flux of previously trapped electrons to hit the wall. These hot electrons induce more than one secondary on average, causing a net loss of electrons from the wall. The sheath collapse quenches when the surface charge becomes positive because the attractive field inhibits further electrons from escaping. Sheath instabilities influence the current balance, energy loss, cross-B-field transport and even the bulk plasma properties. Implications for discharges including Hall thrusters are discussed. More generally, the results show that common theories that treat emission as a fixed (time-independent) "coefficient" do not capture the full extent of SEE effects.

Authors:
Publication Date:
Research Org.:
Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)
Sponsoring Org.:
USDOE Office of Science (SC)
OSTI Identifier:
1059251
Report Number(s):
PPPL-4840
DOE Contract Number:  
DE-ACO2-09CH11466
Resource Type:
Technical Report
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; 70 PLASMA PHYSICS AND FUSION TECHNOLOGY; Ssurface Physics, Oscillations, Double Layers, Computer Simulation

Citation Formats

M.D. Campanell, A.V. Khrabrov and I.D. Kaganovich. Instability, Collapse and Oscillation of Sheaths Caused by Secondary Electron Emission. United States: N. p., 2013. Web. doi:10.2172/1059251.
M.D. Campanell, A.V. Khrabrov and I.D. Kaganovich. Instability, Collapse and Oscillation of Sheaths Caused by Secondary Electron Emission. United States. https://doi.org/10.2172/1059251
M.D. Campanell, A.V. Khrabrov and I.D. Kaganovich. 2013. "Instability, Collapse and Oscillation of Sheaths Caused by Secondary Electron Emission". United States. https://doi.org/10.2172/1059251. https://www.osti.gov/servlets/purl/1059251.
@article{osti_1059251,
title = {Instability, Collapse and Oscillation of Sheaths Caused by Secondary Electron Emission},
author = {M.D. Campanell, A.V. Khrabrov and I.D. Kaganovich},
abstractNote = {The Debye sheath is shown to be unstable under general conditions. For surface materials with sufficient secondary electron emission (SEE) yields, the surface's current-voltage characteristic has an unstable branch when the bulk plasma temperature (Te ) exceeds a critical value, or when there are fast electron populations present. The plasma-surface interaction becomes dynamic where the sheath may undergo spontaneous transitions or oscillations. Using particle-in-cell simulations, we analyze sheath instabilities occurring in a high Te plasma slab bounded by walls with SEE. As the plasma evolves, whenever the sheath enters an unstable state, its amplitude rapidly collapses, allowing a large flux of previously trapped electrons to hit the wall. These hot electrons induce more than one secondary on average, causing a net loss of electrons from the wall. The sheath collapse quenches when the surface charge becomes positive because the attractive field inhibits further electrons from escaping. Sheath instabilities influence the current balance, energy loss, cross-B-field transport and even the bulk plasma properties. Implications for discharges including Hall thrusters are discussed. More generally, the results show that common theories that treat emission as a fixed (time-independent) "coefficient" do not capture the full extent of SEE effects.},
doi = {10.2172/1059251},
url = {https://www.osti.gov/biblio/1059251}, journal = {},
number = ,
volume = ,
place = {United States},
year = {Thu Jan 03 00:00:00 EST 2013},
month = {Thu Jan 03 00:00:00 EST 2013}
}