Effects of emitted electron temperature on the plasma sheath

It has long been known that electron emission from a surface significantly affects the sheath surrounding that surface. Typical fluid theory of a planar sheath with emitted electrons assumes that the plasma electrons follow the Boltzmann relation and the emitted electrons are emitted with zero energ...

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Bibliographic Details
Published in:Physics of plasmas 2014-06, Vol.21 (6)
Main Authors: Sheehan, J. P., Kaganovich, I. D., Wang, H., Sydorenko, D., Raitses, Y., Hershkowitz, N.
Format: Article
Language:English
Subjects:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY
DISTRIBUTION FUNCTIONS
Electric potential
Electron beams
Electron density
ELECTRON EMISSION
Electron energy
ELECTRON TEMPERATURE
Electrons
Maxwellian distribution
Particle in cell technique
Plasma
Plasma physics
PLASMA SHEATH
Plasma sheaths
SIMULATION
Velocity distribution
Voltage drop
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Summary:It has long been known that electron emission from a surface significantly affects the sheath surrounding that surface. Typical fluid theory of a planar sheath with emitted electrons assumes that the plasma electrons follow the Boltzmann relation and the emitted electrons are emitted with zero energy and predicts a potential drop of 1.03Te/e across the sheath in the floating condition. By considering the modified velocity distribution function caused by plasma electrons lost to the wall and the half-Maxwellian distribution of the emitted electrons, it is shown that ratio of plasma electron temperature to emitted electron temperature significantly affects the sheath potential when the plasma electron temperature is within an order of magnitude of the emitted electron temperature. When the plasma electron temperature equals the emitted electron temperature the emissive sheath potential goes to zero. One dimensional particle-in-cell simulations corroborate the predictions made by this theory. The effects of the addition of a monoenergetic electron beam to the Maxwellian plasma electrons were explored, showing that the emissive sheath potential is close to the beam energy only when the emitted electron flux is less than the beam flux.
ISSN:1070-664X
1089-7674
DOI:10.1063/1.4882260