Help with Bohm's Criterion: Pre-Sheath Explained

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In summary, the conversation discusses Bohm's criterion and the concept of pre-sheath. The characteristics of presheath under the influence of negative ions are explored, with the use of an emissive probe to measure presheath potential drop. It is found that the potential drop and drift speed of positive ions decrease with increasing negative ion concentration. The conversation also mentions the numerical results of the theory for sheath formation in multicomponent plasma and compares it with experimental results.
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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
 

1. What is Bohm's Criterion?

Bohm's Criterion is a scientific principle that describes the conditions necessary for a plasma sheath to form around a charged object in a plasma. It was first proposed by physicist David Bohm in the 1940s.

2. What is a plasma sheath?

A plasma sheath is a thin layer of plasma that forms around a charged object in a plasma. It acts as a barrier between the charged object and the surrounding plasma, and can affect the behavior and properties of the charged object.

3. How is Bohm's Criterion related to plasma sheaths?

Bohm's Criterion provides a quantitative measure of the conditions necessary for a plasma sheath to form around a charged object. It takes into account parameters such as the plasma density, temperature, and the charge of the object to determine the critical conditions for sheath formation.

4. What is meant by "Pre-Sheath" in Bohm's Criterion?

The "Pre-Sheath" in Bohm's Criterion refers to the region between the charged object and the plasma sheath. It is the transitional region where the plasma density and potential change rapidly, leading to the formation of the plasma sheath.

5. Why is understanding Bohm's Criterion important in plasma physics?

Bohm's Criterion is important in plasma physics because it helps scientists understand the formation and behavior of plasma sheaths, which play a crucial role in many plasma-based technologies. It also provides a basis for further research and development in the field of plasma physics.

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