Snapshots of the charge density ρ_c in hydrodynamic simulations with multi-wavelength initial perturbations, extracted at an equivalent non linear stage defined by a fixed normalised mixing layer thickness, ∆h/L_x ≃ 0.35. From left to right, the panels show increasing coupling strength (α = 0, weak, intermediate, and strong coupling). All snapshots are shown using the same spatial window and colour scale. The density of the charge fluid ρ_c is given in units of the ρ_c1, the lighter fluid.