Collision-dominated plasma (stellar coronae)

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Discussion Overview

The discussion revolves around the concept of collision-dominated plasmas, particularly in the context of stellar coronae and their diagnostic properties as described in a specific paper on helium-like ions. Participants explore the definitions and implications of collision-dominated versus photoionized plasmas, touching on thermal and non-thermal equilibrium states.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • Some participants suggest that collision-dominated plasmas are indicative of thermal equilibrium, while photoionized plasmas are seen as non-thermal.
  • One participant proposes that collision-dominated plasmas likely have higher density.
  • Another participant speculates that high rates of collisions in gases lead to thermal stability, which may be what is meant by "collision dominated."
  • A participant with a background in plasma physics notes that the term 'collision-dominated' in the referenced paper does not relate to thermal equilibrium, highlighting a potential misunderstanding of the terminology.
  • This participant also points out that collisionless plasmas can still achieve thermal equilibrium, suggesting a more complex relationship between collisions and thermal states.

Areas of Agreement / Disagreement

Participants express differing views on the relationship between collision-dominated plasmas and thermal equilibrium, indicating a lack of consensus on the definitions and implications of these terms.

Contextual Notes

There are unresolved assumptions regarding the definitions of thermal and non-thermal plasmas, as well as the specific context in which the terms are used in the referenced paper. The discussion reflects varying levels of familiarity with the jargon specific to astrophysical plasmas compared to other fields.

atomiclaser
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I was reading some astrophysics paper, they said "Collision-dominated plasmas (e.g. stellar coronae), photo-ionized plas-mas (e.g. AGNs) or transient plasmas (e.g. SNRs) are considered."
Does anyone know what is the difference between these plasmas? for example, temperature, density, charge state etc.
Naively, "collision-dominated " means like ion-atom charge exchange is dominant ?
The paper is "Helium-like ions as powerful X-ray plasma diagnostics"
Proceedings of “X-ray Astronomy 2000”, Palermo, Sep. 2000
ASP Conference Series, Vol. TBD (in press), 2001
R. Giacconi, L. Stella, S. Serio
[Mentors note: arXiv link at https://arxiv.org/abs/astro-ph/0012218v2]

By the way, why the resonant emission, intercombination emission and forbidden emission of He-like ions are very diagnostical tool for high temeprature plasma?
 
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I'm not an expert but collision dominated sounds like a thermal plasma (i.e. in thermal equilibrium) and photoionized sounds like non-thermal.
 
Presumably "collision dominated" plasmas have higher density.
 
sunrah said:
I'm not an expert but collision dominated sounds like a thermal plasma (i.e. in thermal equilibrium) and photoionized sounds like non-thermal.
could you explain more what you mean " thermal plasma (i.e. in thermal equilibrium) and photoionized sounds like non-thermal. "?
 
sunrah said:
could you explain more what you mean " thermal plasma (i.e. in thermal equilibrium) and photoionized sounds like non-thermal. "?

I'm just guessing really.

Normally, in a gas say, high rate of collisions leads to thermal stability or local thermodynamic equilibrium, as it is the only way to distribute energy among neutral particles. I'm just guessing this is what the plasma physicists mean when they say "collision dominated".
If photoionoized is distinct from this, then I think it will be in non-thermal equilibrium, i.e. ions are colder than the electrons.

Theses two cases (thermal EQ and non thermal EQ) actually define two classes of plasmas known as thermal and nonthermal plasmas.
 
I did my graduate work in plasma physics, but do not know anything about astrophysical plasmas. I skimmed the paper because it looked interesting, but you should know that every field has their own jargon, and the jargon in this paper is dramatically different than that used in the ionospheric/magnetospheric physics community I was in. My 'guess' as to what those terms meant was incorrect.

On page 3 of the paper - in the paragraph before section 3 - the authors basically tell you what they mean by some of those terms. They are referring to the primary ionization mechanism. The term 'collision-dominated' has nothing at all to do with thermal equilibrium. Indeed, a collisionless plasmas (such as in the Earth's magnetosphere) can be in thermal equilibrium, although for me the most interesting physics is non-equilibrium.
jason
 
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