Magnetic-field evolution during the three main phases of the By800 experiment for t₀ = 140 min, t₁ = 233 min and t₂ = 325 min. The panels show the normalised parallel current, |∇×B ⋅ B|/|B|² (grayscale), and the reconnecting current sheets (CSs; green), identified using the criterion of Eq. (1). Magnetic-field lines are shown with yellow streamlines, and the β = 1 surface is drawn with a dashed red line. We note how the height of the latter has moved from the initial t₀ to the quasi-static timestep t₂, due to the injection of emerging magnetic-loop structures, increasing the volume filled by a subsequently reconnecting CS. The associated movie is available online.