Schematic illustration of the model. The shaded vertical band at ﹩D=z=0﹩ represents the shock. Filled circles designate regions where the magnetic field amplitude B exceeds some constant threshold. The characteristic scale L for variations in B increases with distance D from the shock. Curved lines illustrate the trajectories of two high‐energy particles of different momenta, ﹩p_{1}< p_{2}﹩, becoming magnetized (﹩R_{\mathrm{L}\,}< L﹩) at two different scales.