Illustration of the method used to determine the positions of the folds and corresponding interfold distance law at small radius in a phase-space slice. Top panel: zoom performed around the axis υ_r = 0 in the region dominated by centrifugal force for the (η, n) = (0.5, −1.0) simulation at t = 40. The corresponding phase-space distribution function f(r, υ_r = 0, j = 0.16) is plotted in the lower panel. The black dots give the positions of local maxima estimated with our local quadratic fit, while the blue and red dots provide upper and lower bounds to compute the (very conservative) error bars shown on Fig. 8.