NDLI: Sheath thickness evaluation for collisionless or weakly collisional bounded plasmas

Content Provider	IEEE Xplore Digital Library
Author	Wang, S.-B. Wendt, A.E.
Copyright Year	1973
Abstract	The widely used Child-Langmuir law for sheath thickness evaluation in semi-infinite collisionless plasmas makes the assumptions of quasi-neutrality (n/sub e/=n/sub i/) and zero electric field intensity E=0 at the sheath edge, as well as applying the Bohm criterion for ions entering the sheath. However, through a whole region fluid model, Poisson's equation has been solved numerically for the steady-state solution through the sheath and presheath without these assumptions. With the sheath edge defined, as in the Child-Langmuir law, at the place where the ion velocity is equal to the Bohm velocity, the sheath thickness of a bounded collisionless or weakly collisional plasma has been found with this model in some cases to be much larger than that obtained with the Child-Langmuir Law. The sheath thickness discrepancy is significant under conditions found in low pressure high density plasma (HDP) tools for plasma processing. Results presented indicate that the sheath thickness is very sensitive to the electric field and space charge density at the sheath edge. The electric field and space charge density can be successfully estimated by an intermediate scale matching method, and are used to derive a modified expression for the potential in the sheath that can be solved numerically for sheath thickness. With these results, the matching problem, arising when sheath and plasma are modeled separately, can be overcome.
Sponsorship	IEEE Nuclear and Plasma Sciences Society
Starting Page	1358
Ending Page	1365
Page Count	8
File Size	187433
File Format	PDF
ISSN	00933813
Volume Number	27
Issue Number	5
Language	English
Publisher	Institute of Electrical and Electronics Engineers, Inc. (IEEE)
Publisher Date	1999-10-01
Publisher Place	U.S.A.
Access Restriction	One Nation One Subscription (ONOS)
Rights Holder	Institute of Electrical and Electronics Engineers, Inc. (IEEE)
Subject Keyword	Plasma sheaths Plasma applications Plasma density Plasma materials processing Plasma temperature Plasma measurements Etching Electrons Plasma diagnostics Space charge
Content Type	Text
Resource Type	Article
Subject	Nuclear and High Energy Physics Condensed Matter Physics

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