Top panel: perturbation to the equilibrium density at t = 110 from a driver with δt = 0.58 τ_Ai. The slow wave can be seen at z ∼ 10 and the fast wave train between z ∼ 40 and z ∼ 100, both propagating to the right. The waveguide width is indicated by 2w, and the magnetic field direction by B. Bottom panel: pertubation to the equilibrium density measured along the centre of the waveguide (x = 0) from the above simulation output. The region between the dashed vertical lines denotes the section of the signal used for analysis of the fast wave train.