On the dynamics of particles in tokamak magnetic field and in RF fields

The motion of magnetically trapped particles and their interaction with an RF field is discussed; for the description a suitable canonical formalism is used. The chosen form of the Hamiltonian allowed to investigate in a relatively simple way the effect of RF fields on the change in the parallel and perpendicular velocities of particles, and, consequently, on the form of the banana and on its radial displacement. Special attention is devoted to the stochastic instability regime. A simple numerical discussion of the interaction of Alfven waves with banana-trapped particles is presented, together with the estimation of the stochastic instability threshold. (author). 7 figs., 36 refs