Oscillating plasma bubbles. III. Internal electron sources and sinks

Journal Article · Wed Aug 15 04:00:00 EDT 2012 · Physics of Plasmas

DOI:https://doi.org/10.1063/1.4743021· OSTI ID:22085998

Stenzel, R L; Urrutia, J M ^[1]

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1. Department of Physics and Astronomy, University of California, Los Angeles, California 90095-1547 (United States)

An internal electron source has been used to neutralize ions injected from an ambient plasma into a spherical grid. The resultant plasma is termed a plasma 'bubble.' When the electron supply from the filament is reduced, the sheath inside the bubble becomes unstable. The plasma potential of the bubble oscillates near but below the ion plasma frequency. Different modes of oscillations have been observed as well as a subharmonic and multiple harmonics. The frequency increases with ion density and decreases with electron density. The peak amplitude occurs for an optimum current and the instability is quenched at large electron densities. The frequency also increases if Langmuir probes inside the bubble draw electrons. Allowing electrons from the ambient plasma to enter, the bubble changes the frequency dependence on grid voltage. It is concluded that the net space charge density in the sheath determines the oscillation frequency. It is suggested that the sheath instability is caused by ion inertia in an oscillating sheath electric field which is created by ion bunching.

• OSTI ID: 22085998
• Journal Information: Physics of Plasmas, Journal Name: Physics of Plasmas Journal Issue: 8 Vol. 19; ISSN PHPAEN; ISSN 1070-664X
• Country of Publication: United States
• Language: English

Related Subjects

70 PLASMA PHYSICS AND FUSION TECHNOLOGY
AMPLITUDES
BUBBLES
ELECTRON DENSITY
ELECTRON SOURCES
FILAMENTS
FREQUENCY DEPENDENCE
HARMONICS
ION DENSITY
IONS
LANGMUIR FREQUENCY
LANGMUIR PROBE
PLASMA
PLASMA INSTABILITY
PLASMA POTENTIAL
PLASMA SHEATH
PLASMA WAVES
SPACE CHARGE
SPHERICAL CONFIGURATION