Criterion of sheath formation in magnetized low pressure plasma

A criterion of sheath formation is obtained for magnetized low pressure plasmas. The criterion includes the effect of both collision and the magnetic field. The collision parameter is defined by the ratio of the ionization length to the ion mean free path. The ionization frequency is assumed to be c...

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Bibliographic Details
Published in:Physics of plasmas 2017-11, Vol.24 (11)
Main Authors: Moulick, R., Adhikari, S., Goswami, K. S.
Format: Article
Language:English
Subjects:
Bohm criterion
Charge deposition
Collision parameters
Dependence
Field strength
Ionization
Low pressure
Magnetic fields
Plasma physics
Plasmas (physics)
Sheaths
Space charge
Validity
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Summary:A criterion of sheath formation is obtained for magnetized low pressure plasmas. The criterion includes the effect of both collision and the magnetic field. The collision parameter is defined by the ratio of the ionization length to the ion mean free path. The ionization frequency is assumed to be constant. The condition obtained is consistent with the electrostatic case. In the absence of the magnetic field and the collision, it retrieves the Bohm criterion at the sheath edge. For an electrostatic case in the absence of ion neutral collision, the Bohm criterion determines the ion entry speed within the sheath. However, the presence of collision limits the validity of the criterion to a threshold value of the collision parameter. In the magnetized scenario, the validity is found to be dependent on the magnetic field angle besides the collision parameter. Even in a collisionless scenario, the validity is in question depending on the field angle. A critical collision parameter is found for a definite magnetic field strength beyond which there is no more angle dependency on the validity criterion. The effect of the magnetic field on the space charge deposition is highlighted.
ISSN:1070-664X
1089-7674
DOI:10.1063/1.4994261