Ion flow and sheath structure near positively biased electrodes

What effect does a dielectric material surrounding a small positively biased electrode have on the ion flow and sheath structure near the electrode? Measurements of the ion velocity distribution function and plasma potential near positively biased electrodes were made using laser-induced fluorescenc...

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Bibliographic Details
Published in:Physics of plasmas 2016-11, Vol.23 (11)
Main Authors: Hood, R., Scheiner, B., Baalrud, S. D., Hopkins, M. M., Barnat, E. V., Yee, B. T., Merlino, R. L., Skiff, F.
Format: Article
Language:English
Subjects:
Cathodes
Dielectrics
Distribution functions
Electrodes
Ion velocity
Laser induced fluorescence
Particle in cell technique
Plasma physics
Potential barriers
Sheaths
Velocity distribution
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Summary:What effect does a dielectric material surrounding a small positively biased electrode have on the ion flow and sheath structure near the electrode? Measurements of the ion velocity distribution function and plasma potential near positively biased electrodes were made using laser-induced fluorescence and an emissive probe. The results were compared with 2D particle-in-cell simulations. Both measurements and simulations showed that when the positive electrode was surrounded by the dielectric material, ions were accelerated toward the electrode to approximately 0.5 times the ion sound speed before being deflected radially by the electron sheath potential barrier of the electrode. The axial potential profile in this case contained a virtual cathode. In comparison, when the dielectric material was removed from around the electrode, both the ion flow and virtual cathode depth near the electrode were dramatically reduced. These measurements suggest that the ion presheath from the dielectric material surrounding the electrode may enclose the electron sheath of the electrode, resulting in a virtual cathode that substantially influences the ion flow profile in the region.
ISSN:1070-664X
1089-7674
DOI:10.1063/1.4967870