Electron-rich sheath dynamics. I. Transient currents and sheath-plasma instabilities

Journal Article · Wed Jun 15 04:00:00 EDT 2011 · Physics of Plasmas

DOI:https://doi.org/10.1063/1.3601858· OSTI ID:21546942

Stenzel, R L ^[1]; Gruenwald, J; Ionita, C; Schrittwieser, R ^[2]

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1. Department of Physics and Astronomy, University of California, Los Angeles, California 90095-1547 (United States)
2. Institute for Ion Physics and Applied Physics, University of Innsbruck, A-6020 Innsbruck (Austria)

The evolution of an electron-rich sheath on a plane electrode has been investigated experimentally. A rapidly rising voltage is applied to a plane gridded electrode in a weakly ionized, low temperature, and field-free discharge plasma. Transient currents during the transition from ion-rich to electron-rich sheath are explained including the current closure. Time-resolved current-voltage characteristics of the electrode are presented. The time scale for the formation of an electron-rich sheath is determined by the ion dynamics and takes about an ion plasma period. When the ions have been expelled from the sheath a high-frequency sheath-plasma instability grows. The electric field contracts into the electron-rich sheath which implies that the potential outside the sheath drops. It occurs abruptly and creates a large current pulse on the electrode which is not a conduction but a displacement current. The expulsion of ions from the vicinity of the electrode lowers the electron density, electrode current, and the frequency of the sheath-plasma oscillations. Electron energization in the sheath creates ionization which reduces the space charge density, hence sheath electric field. The sheath-plasma instability is weakened or vanishes. The ionization rate decreases, and the sheath electric field recovers. A relaxation instability with repeated current transients can arise which is presented in a companion paper. Only for voltages below the ionization potential a quiescent electron rich-sheath is observed.

• OSTI ID: 21546942
• Journal Information: Physics of Plasmas, Journal Name: Physics of Plasmas Journal Issue: 6 Vol. 18; ISSN PHPAEN; ISSN 1070-664X
• Country of Publication: United States
• Language: English

Related Subjects

70 PLASMA PHYSICS AND FUSION TECHNOLOGY
ELECTRIC CONDUCTIVITY
ELECTRIC FIELDS
ELECTRICAL PROPERTIES
ELECTRODES
ELECTRON DENSITY
INSTABILITY
IONIZATION
IONIZATION POTENTIAL
PHYSICAL PROPERTIES
PLASMA INSTABILITY
PLASMA SHEATH
PLASMA WAVES
SPACE CHARGE
TRANSIENTS