SUPERBANANA ORBITS AND REDISTRIBUTION OF MARGINALLY TRAPPED FAST IONSDURING SAWTOOTH CRASHES

The work represents the first step in studying the effect of sawtooth crashes on the ''resonant'' fast ions, i.e., the ions that are trapped or marginally untrapped with respect to the helical perturbation asso ciated with the sawtooth crash. The simplest case is considered, when the particles in the absence of perturbations are marginally trapped i n the tokamak magnetic field and characterized by narrow orbits. It is shown that in the presence of perturbation the guiding centers of the banana orbits oscillate in the toroidal and radial directions, formin g ''superbanana'' orbits. The radial width of such ''superbananas'' co nstitutes a significant part of the sawtooth mixing radius, which impl ies that sawteeth can strongly redistribute these particles. (C) 1998 American Institute of Physics.