Bucket transport of energetic ions in tokamaks

Abstract

The so-called “bucket transport” of energetic ions — the spatial mixing of these ions due to spatial displacement of resonances — is studied with special attention to quasi-steady-state magnetic perturbations. A Hamiltonian formalism suitable to the case when the resonance displacement results from the collisional slowing down of the particles and the temporal evolution of the safety factor profile is suggested. The energy flux produced due to the bucket transport is shown to be considerable in configurations with low shear. It is shown that the bucket transport flux associated with magnetic islands tends to be localized at some distance from the islands. The bucket transport caused by perturbations with non-zero frequencies is also discussed.