Long-term time evolution of the pitch angle for particle orbits with initial pitch angles 160.4° (subcritical, a)), 159.0° (critical, b)), and 155.4° (supercritical, c)). Due to the large number of bounces, only the maxima and minima of the pitch angle curves are shown for the particle orbit plots b) and c). Particle orbits with subcritical angles escape, whereas particles with supercritical angles and above remain trapped.