# Collision-dominated plasma (stellar coronae)

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## Summary:

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 ?

## Main Question or Discussion Point

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.

mathman
Presumably "collision dominated" plasmas have higher density.

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. "?

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.

jasonRF