Type of orbit followed by a particle as a function of its initial position (D, Y_i). The regions are coloured according to the value of ρ_C(D,Y_i), and the level ρ_C = 1 is represented by the black line. The types of orbits are labelled as in (Eq. (20)). The magenta dashed line shows the initial position of the trajectory reaching the minimum radius over the whole vertical line. For D < D_crit, it is a trajectory of type T₂. For D > D_crit, it is a trajectory of type T₁ but infinitely close to the ρ_C = 1 curve (see text).