Theory of fast ion transport during sawtooth crashes in tokamaks

摘要

An approach is suggested for the description of fast ion transport in tokamaks during sawtooth crashes, which takes into account the orbital motion of the particles and the temporal evolution of the magnetic configuration. The approach is based on a kinetic equation for the distribution function of fast ions derived using different scales with characteristic times of the sawtooth crash and of the fast ion motion. The evolution of the magnetic configuration in the process of the crash is assumed to be known, and its analytical description is suggested for the case of the Kadomtsev type of crash. The derived kinetic equation is analysed for both trapped and circulating particles, and conclusions are drawn concerning redistribution of particles of various energies and pitch angles during crashes. The physical nature of fast ion transport induced by the sawtooth crash is elucidated.