Stochastic Behavior of Particles in a Circularly Polarized Standing Wave

The particle motion in a standing left circularly polarized wave is studied. For wave frequency lower than the ion cyclotron frequency ωci, the slow varying trajectory is given by the ponderomotive force FNL=q2∇|E|2/[mω(ω-Ωci)]. However, for ω close to Ωci, stochastic trajectories occur. These stochastic trajectories are due to the overlapping of closed orbits due to each of the propagating waves which form the standing wave.