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A strongly coupled plasma is characterized by the following attributes:

  • higher number density
  • lower particle speeds (lower temperature)
  • smaller Debye length
  • continuous electrostatic influence throughout, stronger long range interaction
  • sparsely populated Debye sphere (lower Debye Number)

Likewise, weakly coupled plasmas are characterized by the inverse attributes:

  • lower number density
  • higher particle speeds
  • larger Debye length
  • only occasional electrostatic influence, weaker long range interaction
  • densely populated Debye sphere (higher Debye number)

The number density within the Debye sphere directly contrasts with the overall number density. Does this imply that a weakly coupled plasma has Debye-sphere-sized pockets of high density plasma within the greater, low-density plasma medium? Likewise, does this imply that a strongly coupled plasma has Debye-sphere-sized pockets of low density plasma within the greater, high-density plasma medium?

At first I thought it could be up to the size of the Debye sphere but sources clearly state density not just population.

Sources: https://farside.ph.utexas.edu/teaching/plasma/Plasma/node7.html

https://en.wikipedia.org/wiki/Plasma_parameter

https://www.chemeurope.com/en/encyclopedia/Plasma_parameter.html

Similar question but without a direct answer: How is it possible that a collisionless plasma has a more densely populated Debye sphere?

TrapAlcubierreDrive
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1 Answers1

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I would not go as far as you do in your conclusions. I think the confusion comes from the wording "densely populated" which does not mean "high density". The constraint on the populations of the Debye's sphere just add a compatible constraint onto the densities. Let's take:$ \rho _{s};\lambda _{s} $ for strongly coupled plasma and :$ \rho _{w};\lambda _{w} $ for a weakly coupled one.

The population of the Debye Sphere is given by: $$ N_{D}= \rho .V \sim \rho. \lambda _{D} ^{3}$$

And we are given: $$\begin{cases}\lambda _{s} << \lambda _{w}\\\rho_{s} >> \rho_{w}\\ N_{w} >> N_{s}\end{cases}$$

The question is to know if all these constraints are compatible. It comes:

$$ \frac{ N_{s} }{ N_{w} } = \frac{ \rho _{s} }{ \rho _{w} } \big( \frac{ \lambda _{s} }{ \lambda _{w} } \big)^{3}$$

But: $\begin{cases}\frac{ \rho _{s} }{ \rho _{w} } \gg 1\\\frac{ \lambda _{s} }{ \lambda _{w} } \ll 1\end{cases} $ is not incompatible with:$ N_{s} \ll N_{w} $

Shaktyai
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