Current sheets as waveguides for the fast magnetosonic wave

The geometry of rays and wavefronts associated to the fast magnetosonic wave is studied for a planar cold plasma, in an equilibrium where magnetic null points and current sheets are present. It is found (a) that null points attract rays and singular ones repel them, causing a characteristic evolution of wavefronts; and (b) that current sheets act as waveguides, directing both rays and wavefronts towards them. High frequency fast waves remain continuous when crossing the sheet; depending on the initial condition, these waves may become shocks before or after the sheet.