Trying to apply electric current to plasmas in motion.

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Discussion Overview

The discussion revolves around the application of electric current to plasmas in motion, particularly in the context of fluorescent lighting. Participants explore the relationship between electric potential, ionization of gases, and the behavior of plasma within a containment system.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Homework-related

Main Points Raised

  • Doug Ettinger questions how to represent a mass of plasma traveling from point A to point B as electrical current "I".
  • Doug Ettinger draws a parallel to fluorescent lighting, asking if there are laws that describe the ionization of gas due to electric potential.
  • Another participant notes that the current in the plasma is equal to the current in the power supply circuit of a fluorescent light but expresses uncertainty about the relevant equations for confined plasma in different situations.
  • Doug Ettinger inquires about the mechanism of ionization in fluorescent lights and the necessity of ballast devices.
  • A later reply explains the operation of fluorescent lights, detailing the thermionic emission of electrons from the cathode, interactions with mercury atoms, and the role of ballasts in limiting current due to negative differential resistance.

Areas of Agreement / Disagreement

Participants express uncertainty regarding the specific equations and laws governing the behavior of plasma in motion and its relationship to electric current. There are multiple viewpoints on the mechanisms involved in fluorescent lighting, but no consensus is reached on the broader application to other plasma scenarios.

Contextual Notes

Limitations include a lack of specific equations for confined plasma in different situations and the dependence on the definitions of terms like "current" and "ionization" in various contexts.

dougettinger
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How do you represent a certain mass of plasma (ions and free electrons) traveling inside a containment from point A to point B as "I", electrical current?

Trying to make a connection, Doug Ettinger
 
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I seem to be drawing a blank. Perhaps someone knows about flourescent lighting. Electric potential between the ends of a flourescent light causes the gas inside to be ionized. Are there any laws for describing what happens ?

Ionizingly, Doug Ettinger
 
The current flowing through he plasma is equal to the current flowing through the rest of the power supply circuit in a florescent light. However I don't know the equations for determining this in a confined plasma in a different situation.
 
How does a flourescent light work? Does the heat from the current ionize a certain gas that is enclosed inside the lamp? Why does flourescent lighting require ballast devices?

Learning more about plasma, Doug Ettinger
 
A flourescent light works because as the cathode is heated, it thermionically emits electrons which undergo collisions with vaporized Mercury atoms. As the Mercury atoms de-excite, they release a UV photon. This photon then interacts with the phosphor on the wall of the chamber causing it to emit visible light.

They require a ballast because they have negative differential resistance. This means that as more current is applied to the fluorescent tube, the resistivity actually decreases. This is dangerous because there is no limit to the amount of current running through the tube.

A ballast is connected in parallel with the fluorescent tube to limit the current running through it. There are many kinds, but the simplest is an inductor placed in series with the fluorescent lamp and the starter.

The starter is a device that provides a voltage spike to the tube to initiate the discharge.
 

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