Averaged magnetic field as a function of time and resolution for the cases with χ_c = 0.5 (left) and χ_c = 0.1 (right). Solid lines represent simulations in which the ion-neutral collisional interaction is taken into account (without charge-exchange). Dotted lines represent simulations without collisional coupling. Green, blue, purple, and red colours correspond to simulations with N₀ = 250, 500, 1000, 2000, respectively. The vertical dashed lines approximately mark the separation between the linear and non-linear phases of the instability. The inset in each panel shows a zoom of the interval τ ∈ [5, 15].