Vertical cuts through the loop axis showing the vertical structure of the Alfvén wave. Upper two panels: kinetic (left) and magnetic (right) wave energy, integrated in time over a full period. Lower left panel: sum of the two components of wave energy and lower right panel: analogous plot using data from straight field (no magnetic field expansion) experiments. In each case, we have normalised using the total Alfvén wave energy present in the respective simulation.