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Plasma coupling parameter |
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:<math> \epsilon_p = \Lambda^{-1}\ </math>.
== Coupling parameter ==
A closely related parameter is the plasma coupling <math>\Gamma</math>, defined as a ratio of the Coulomb energy to the thermal one:
:<math> \Gamma = \frac{E_\mathrm{C}}{kT_e} </math>.
The Coulomb energy (per particle) is
:<math> E_\mathrm{C} = \frac{q_e^2}{4\pi\epsilon_0\langle r \rangle}</math>,
where for the typical inter-particle distance <math>\langle r \rangle</math> usually is taken the [[Wigner-Seitz radius]]. Therefore,
:<math> \Gamma = \frac{q_e^2}{4\pi\epsilon_0 kT_e}\sqrt[3]{\frac{4\pi n_e}{3}} </math>.
Clearly, up to a numeric factor of the order of unity,
:<math> \Gamma \sim \Lambda^{-2/3}\ </math>.
In general, for multicomponent plasmas one defines the coupling parameter for each species ''s'' separately:
:<math> \Gamma_s = \frac{q_s^2}{4\pi\epsilon_0 kT_s}\sqrt[3]{\frac{4\pi n_s}{3}} </math>.
Here, ''s'' stands for either electrons or (a type of) ions.
== The ideal plasma approximation ==
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