Dilution and Zeff due to fixed fraction impurities

[tbody-cfs]

The dilution due to fixed fraction impurities is not computed, nor are the modifications to the heat conductivity and resistivity.

For this, we'd need to compute the mean charge as a function of temperature — can get this out of radas.

Then, ne = ni * Zi + ne * cz * <Zz(Te)> so ni = ne/Zi (1 - cz * <Zz(Te)>). For this, we probably need to modify the quasineutrality component.

The impurities will also change Zeff, which in turn changes the resistivity and heat conductivity. The expressions for these can be found in https://doi.org/10.1088/1741-4326/ac0412