MHD wave dynamics close to a current sheet

Using the WKB approximation, the propagation of fast magnetoacoustic waves close to a Y-point of a current sheet is analyzed. When the presence of a small (of order ?), uniform magnetic field Bz parallel to the current, with the role of a perturbation, is taken into account, weak chaos of the ray trajectories is found. The properties of the system are then analyzed by means of a mapping of the Poincaré section. It is found that the region of stochasticity for very small ? fills almost the whole phase space, and decreases with increasing ?.