The influence of collisions on the plasma sheath transition

Journal Article · Sat Nov 01 04:00:00 EST 1997 · Physics of Plasmas

DOI:https://doi.org/10.1063/1.872536· OSTI ID:544870

Riemann, K ^[1]

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1. Lehrstuhl fuer Theoretische Physik 1, Ruhr-Universitaet Bochum, D-44780 Bochum (Germany)

In the asymptotic limit {lambda}{sub D}/{lambda}{r_arrow}0 (where {lambda}{sub D} is the electron Debye length and {lambda} represents the ion mean free path) the boundary layer of a collision dominated plasma is split up in a collision free planar sheath (scale {lambda}{sub D}) and a quasi-neutral presheath (scale {lambda}). The {open_quotes}sheath edge{close_quotes} separating the presheath and the sheath is defined by the Bohm criterion. To clear up controversial statements on the validity of the plasma sheath concept and on the role of the Bohm criterion for finite values of {lambda}{sub D}/{lambda}, a simple fluid model of the ions is used to account for collisions and for space charges in the boundary layer. It is shown that the asymptotic solution on an {open_quotes}intermediate scale{close_quotes} (scale length {lambda}{sup 1/5}{lambda}{sub D}{sup 4/5}) is suitable to match the presheath and sheath solutions smoothly and to construct a convenient approximation for small but finite {lambda}{sub D}/{lambda}. The intermediate scale, again, is closely related to the Bohm criterion. Various attempts to derive a {open_quotes}generalized{close_quotes} Bohm criterion accounting for collisions are inconsistent. {copyright} {ital 1997 American Institute of Physics.}

• OSTI ID: 544870
• Journal Information: Physics of Plasmas, Journal Name: Physics of Plasmas Journal Issue: 11 Vol. 4; ISSN PHPAEN; ISSN 1070-664X
• Country of Publication: United States
• Language: English

Related Subjects

70 PLASMA PHYSICS AND FUSION TECHNOLOGY
ION COLLISIONS
PLASMA SHEATH
SIMULATION