Decay-time constant τ vs. longitudinal separation Δϕ (as given by Equation (2)) for ∼25 MeV protons. The start of the decay phase is defined as when intensities return to 50% of I_p. The coloured lines connect s/c data points for a single event. The grey shading shows results from a 25 MeV simulation run following the method of Hutchinson et al. (2023b). The error bars were omitted when they are smaller than the data points.