Help with Bohm's Criterion: Pre-Sheath Explained

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Bohm's criterion relates to the formation of a pre-sheath in plasma physics, particularly in the presence of negative ions. The pre-sheath potential drop is measured using an emissive probe, revealing that this potential drop and the drift speed of positive ions decrease as negative ion concentration increases. The discussion highlights numerical results that align with experimental findings regarding sheath formation in multicomponent plasma. Understanding these dynamics is crucial for applications in plasma technology and research. The impact of negative ions on pre-sheath characteristics is a key focus of the investigation.
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Hi,
I do not know if this is the right section to post my question. Anyway here I go..
Can anyone give a brief explanation of Bohm's criterion, that is the concept of pre-sheath.
Thank you.
 
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the characteristics of presheath under the influence of negative ions have been investigated. An emissive probe is used to measure presheath potential drop in front of an ion-rich sheath. Presheath potential drop and the drift speed of positive ions are found to decrease with increasing negative ion concentration. The numerical results of the theory for sheath formation in multicomponent plasma is discussed and compared with experimental results.

Keywords: Presheath; Negative ions; Bohm speed
 

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