Simulation setup for 23 flux ropes merging. The figure shows current density in the midplane z = L/ 2, taken from the early stage of the MHD simulations. The central rope is the unstable flux rope (λ = 1.8) while the rest are stable (λ = 1.4). Note that the central unstable flux rope shows signs of the initial kink instability, with a current sheet forming at the right-hand side of the loop. Originally published in Hood et al. (2016).