CHAOTIC SCATTERING OFF A ROTATING TARGET

We study the classical scattering of a point particle from one and two rotating hard discs in a plane, as an idealization of the scattering off a rotating target. The system displays regular or chaotic behaviou r depending on the value of the only constant of motion: the Jacobi in tegral. We present results on the transition between regular and chaot ic behaviour in terms of the periodic orbits of the system. For certai n ranges of the Jacobi integral the dynamics is fully hyperbolic. The number of symbols needed to characterize the invariant set is differen t in each of those intervals and may become arbitrarily high.