Spatially averaged magnetic field as a function of ionisation degree for simulations with N₀ = 500 and different values of total density, ρ_T. Symbols and lines correspond to simulations with α_eff = 0 and α_eff = α, respectively. The blue dotted, grey dashed-dotted, and red dashed lines represent the cases with ρ_T = 10⁻¹¹,  10⁻¹⁰ and 10⁻⁹ kg m⁻³, respectively. The black line corresponds to the prediction of the single-fluid model.