Current collection by a cylindrical probe in a partly ionized, collisional plasma

Journal Article · Sat Jul 15 04:00:00 EDT 2006 · Physics of Plasmas

DOI:https://doi.org/10.1063/1.2208620· OSTI ID:20860149

Pletnev, V; Laframboise, J G ^[1]

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1. Department of Physics and Astronomy, York University, Toronto M3J 1P3 (Canada)

A numerical calculation of ion and electron current collection by a cylindrical Langmuir probe in a partly ionized plasma has been done. The effect of electron and ion collisions with neutrals on the current collected by the probe has been investigated. The validity of the collisionless theory of Laframboise [J. G. Laframboise, University of Toronto, Institute for Aerospace Studies, UTIAS Report No. 100 (1966)] has been studied. The iterative scheme of Laframboise has been combined with Monte Carlo solution of the Boltzmann equation to provide self-consistent steady-state electron and ion density and electric potential distributions as functions of radius. Our model includes elastic ion-neutral and electron-neutral collisions, ionization of neutrals by electron impact, energy loss of electrons due to excitation and ionization of neutrals, and charge-exchange collisions. Our model has been demonstrated by calculating the current collection by a probe in a nitrogen plasma, but it can be applied in other cases because we avoided adjustable parameters. Our results confirm published experimental data which indicate that Laframboise's theory can be applied when the attracted particles are electrons and ionization processes do not play an important part. When the attracted particles are ions, it is found that charge-exchange collisions in the sheath produce by far the largest contribution to the increase in their collection current. For this situation, collisionless theory can be applied only when the mean distance traveled by ions inside the sheath is much less than the mean free path. The condition that the sheath size is much smaller than the mean free path does not guarantee a collisionless sheath near a cylindrical probe. This condition is in good agreement with experimental results in the literature.

• OSTI ID: 20860149
• Journal Information: Physics of Plasmas, Journal Name: Physics of Plasmas Journal Issue: 7 Vol. 13; ISSN PHPAEN; ISSN 1070-664X
• Country of Publication: United States
• Language: English

Related Subjects

70 PLASMA PHYSICS AND FUSION TECHNOLOGY
BOLTZMANN EQUATION
CHARGE EXCHANGE
COLLISIONAL PLASMA
CYLINDRICAL CONFIGURATION
ELECTRIC CURRENTS
ELECTRIC POTENTIAL
ELECTRONS
EXCITATION
ION COLLISIONS
ION DENSITY
IONIZATION
IONS
ITERATIVE METHODS
LANGMUIR PROBE
MATHEMATICAL SOLUTIONS
MEAN FREE PATH
MONTE CARLO METHOD
NITROGEN
PLASMA DENSITY
PLASMA SHEATH
RADIATION TRANSPORT
STEADY-STATE CONDITIONS