Examining the range of validity of the Bohm criterion

Crespo, R. Morales; Franklin, R N

doi:10.1017/s0022377814000038

Cited by 6 publications

(4 citation statements)

References 20 publications

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“…Extensions exist for multiple ion species, [34] including negative ions, [35] but the classical result will be used in this model. Although the Bohm velocity is a widely known result in low temperature plasma physics, the applicability of it to any system that deviates from the strict conditions from which it is derived is a topic of ongoing contention, [36][37][38][39][40][41] and researchers should use caution when using a value for the Bohm velocity for anything but the most basic of plasmas.…”

Section: Analytical Derivationmentioning

confidence: 99%

Concepts, Capabilities, and Limitations of Global Models: A Review

Hurlbatt

Gibson

Schröter

et al. 2016

Plasma Processes & Polymers

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For researchers wishing to generate an understanding of complex plasma systems, global models often present an attractive first step, mainly due to their ease of development and use. These volume averaged models are able to give descriptions of plasmas with complex chemical kinetics, and without the computationally intensive numerical methods required for spatially resolved models. This paper gives a tutorial on global modeling, including development and techniques, and provides a discussion on the issues and pitfalls that researchers should be aware of. Further discussion is provided in the form of two reviews on methods of extending global modeling techniques to encompass variations in either time or space.

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Section: Analytical Derivationmentioning

confidence: 99%

Concepts, Capabilities, and Limitations of Global Models: A Review

Hurlbatt

Gibson

Schröter

et al. 2016

Plasma Processes & Polymers

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show abstract

“…On the other hand, the ratio of electron and ion flux density into their respective sheaths can be measured directly by area scanning of an asymmetric double probe. With ion sheath characteristics being well-studied [4,[22][23][24][25][26][27][28][29][30][31][32][33][34][35], the electron flux density can be at least inferred from A i /A e , thus experimentally testing whether the predictions associated with the electron Bohm criterion applies to known Langmuir probe techniques. Previous studies have been focused on perturbations of global plasma parameters via area scanning of an electrode biased with respect to the grounded chamber wall [7].…”

Section: Introductionmentioning

confidence: 99%

Direct measurement of ion and electron flux ratio at their respective sheath-edges and absence of the electron Bohm criterion effects

Jin¹,

Yip²,

Zhang³

et al. 2022

Plasma Sources Sci. Technol.

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A recent theory suggest that electrons enter electron sheaths at an electron Bohm velocity given by (Te/me)1/2 instead of the electron thermal velocity as conventionally assumed. To test this theory, the flux density ratio Γe,se/Γi,se of electrons and ions entering their respective sheaths was directly measured via an almost continuous Ai/Ae area ratio scanning. The measured value agrees with the predictions assuming electrons entering the electron sheaths at their thermal velocity. The predictions associated with the electron Bohm criterion has not been found. If the predictions of such theories are true, the electron or ion presheath density drops will be very different from conventionally expected values.

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“…It is easy to show that even expressions like (57) are in agreement with the classical formulation of the Bohm criterion. As has been shown in [21] these kinds of expression are deduced from the misleading assumption that Sagdeev's potential has a maximum value at the sheath edge when λ λ ≠ / 0 D b . To show that (57) is in agreement with the Bohm criterion, we only have to consider the dependence of the electric field at the sheath-edge according to (55), that is y q q ˙r s s b…”

Section: A Modified Bohm Criterion For Plasmas In the Collisional Reg...mentioning

confidence: 99%

The Chodura layer formation in an active and collisional plasma under the action of a constant magnetic field

Crespo¹

2016

Plasma Sources Sci. Technol.

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This paper studies the multi-layer structure of the plasma-sheath transition for an electropositive plasma under the action of a constant and oblique magnetic field. The introduction of the Chodura-scale allows us to introduce the concepts of Chodura-layer, Chodura-edge and Chodura-solution in a natural way as a consequence of a boundary layer structure formalism-in a similar manner to what happens in the plasma-sheath transition. Therefore, the region from the plasma bulk to the wall can be divided in three regions: (i) the plasma-presheath, a quasineutral space region dominated by ionization and/or collisions, (ii) the Chodura-layer, a quasineutral region also dominated by the action of the magnetic field though the drift term and finally (iii) the sheath region. It is shown that if magnetization is the dominant presheath mechanism, it is only located in the Chodura-layer, and this causes the electric field to become singular at the Chodura-edge, between two quasineutral regions-i.e. the plasma-presheath and the Chodura-layer.

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Examining the range of validity of the Bohm criterion

Abstract: This work shows that there is no such thing as a formulation of the Bohm criterion for the case of a collisional plasma. It examines critically the work of several authors who have sought to promote their own version of what has come to be called a collisionally modified Bohm criterion.

Cited by 6 publications

References 20 publications

Concepts, Capabilities, and Limitations of Global Models: A Review

Concepts, Capabilities, and Limitations of Global Models: A Review

Direct measurement of ion and electron flux ratio at their respective sheath-edges and absence of the electron Bohm criterion effects

The Chodura layer formation in an active and collisional plasma under the action of a constant magnetic field

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