Nonlocal behavior of the excitation rate in highly collisional RF discharges

The present work focuses on the fundamental aspects of atmospheric pressure plasma electropositive discharges operated in the ohmically heated mode, the electron heating and the excitation (ionization) rate. We find that the two do not necessarily have similar profiles and can show peaks at differen...

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Bibliographic Details
Published in:Plasma sources science & technology 2015-08, Vol.24 (4), p.44004-11
Main Authors: Eremin, Denis, Hemke, Torben, Mussenbrock, Thomas
Format: Article
Language:English
Subjects:
Adiabatic flow
atmospheric pressure plasma discharge
collisional plasma
Electric discharges
Electric fields
electron heating
energetic electrons
Excitation
glow discharge
Heating
Ionization
Maxima
nonlocal kinetics
ohmic heating
Sheaths
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Summary:The present work focuses on the fundamental aspects of atmospheric pressure plasma electropositive discharges operated in the ohmically heated mode, the electron heating and the excitation (ionization) rate. We find that the two do not necessarily have similar profiles and can show peaks at different locations, the ionization rate being much more sensitive to the electric field compared to the sensitivity to the electric field of the electron heating. This suggests an explanation for the discrepancies between the profiles of the power absorbed by electrons and the excitation patterns previously reported in the literature and observed in the present study. The excitation rate profile can then be explained by analyzing overlapping of the electron heating and the electric field profiles. Surprisingly, it has been discovered that the excitation dynamics exhibits nonlocal behavior having maxima spatially separated from the maxima of the electric field and the electron heating rate, a new effect in discharges operated in the mode. The strong electric field in such discharges leads to large displacements of the electron component. This can produce significant charge separation close to the sheath or even in the bulk plasma because electrons are not able to follow the electric field adiabatically and maintain quasineutrality owing to the high collisionality. In particular, this leads to a significant distortion of the sheath structure and increase in the electric field there.
ISSN:0963-0252
1361-6595
DOI:10.1088/0963-0252/24/4/044004