Evolution of magnetic field model IV, using ζ = 10⁻³. We used a grid of N_r = 60 radial steps and N_θ = 91 polar steps inside the core and N_Exp = 40 external multipoles, and the HHJ EoS. From top to bottom: Configuration of the magnetic field, where lines represent the poloidal magnetic field (labeled by the magnitude of α) and colors the toroidal potential β; χ_n and χ_c, both in units of χ₀ = B₀²/4πn₀μ₀; poloidal component of the neutron velocity, v_n, and ambipolar diffusion velocity, v_ad, where arrows represent the direction and colors the magnitude normalized to R/t₀. Columns correspond to different times: t = 0, t_ζB, 5 t_ζB, 0.1 t_ad, and t_ad.