w never greater than 1 in level populations?

[wkerzendorf]

is that right?

this line level_populations[~self.atom_data.levels.metastable] *= np.min([self.ws, np.ones_like(self.ws)],axis=0) in plasma_array. worth checking

[ssim]

In the context of the approximation being made, I don't think it makes much sense to allow W>1 (this will lead to odd behaviour of populations that are "not metastable" compared to those that are "metastable). Better to limit to W <1 - perhaps flag a warning (likely means that the radiation field model is doing a particularly bad job).