[Mesa-users] The plasma interaction parameter

[Evan Bauer]

Hi Ana,

The quantity "gam" in the profile output is the plasma interaction parameter for ions rather than electrons, so it differs from \Gamma_e by a factor of approximately zbar^(5/3). Does that explain the difference that you're seeing?

Cheers,
Evan

> On Nov 23, 2020, at 3:23 PM, Ana Brito via Mesa-users <mesa-users at lists.mesastar.org> wrote:
> 
> Dear MESA users,
> 
> I have a question about the plasma interaction parameter.
> 
> This parameter can be computed using using the expression:
> 
> \Gamma_e = \frac{e^2}{d k_B T}
> where
> d = ( \frac{3}{4 \pi n_e} )^{1/3}.
> (e is the electron charge, k_B the Boltzmann constant, T the temperature)
> The electron density, n_e, can be obtained from ye (the electron to baryon ratio), one of the profile columns options:
> n_e = ye*rho*AV.
> Here, rho is the density, and AV the Avogadro number.
> 
> In the figure attached I represented this \Gamma_e with a black line for a 1 solar mass main-sequence stellar model. Later I noticed that the plasma interaction parameter is itself a profile output option. The \Gamma_e obtained directly from the profile output is represented in the same figure with a blue line. These two lines do not match. There is a difference between them that I don't know how to explain. Maybe I'm doing something wrong with the electron density. 
> My question is: what could be the cause of this difference between black and blue lines? 
> 
> I am also sending attached the inlist used under MESA v12115. 
> 
> Thank you very much!
> 
> Best regards,
> 
> Ana
> <inlist_solarmass1><starting1.mod><Gamma_e.png>_______________________________________________
> mesa-users at lists.mesastar.org
> https://lists.mesastar.org/mailman/listinfo/mesa-users
>