Canonical transformation for trapped/passing guiding-center orbits in   axisymmetric tokamak geometry
  The generating function for the canonical transformation from the parallel canonical coordinates $(p_{\|},s)$ to the action-angle coordinates $(J,\zeta)$ for trapped/passing guiding-center orbits in axisymmetric tokamak geometry is presented. Drawing on the analogy between the phase-space portraits of the librating/rotating pendulum and the trapped/passing guiding-center orbits, the generating function is expressed in terms of the Jacobi zeta function, which can then readily be used to obtain an explicit expression for the bounce-center transformation for trapped/passing-particles in axisymmetric tokamak geometry. 
Alain J. Brizard and Francois-Xavier Duthoit
physics.plasm-ph