Collisionless diffusion regimes of trapped particles in tokamaks
The collisionless dynamics of trapped particles in a non axisymmetric tokamak configuration with toroidal magnetic field ripple are investigated. The resonances between the particle motion and the perturbation are studied with the Hamiltonian description based on action-angles variables. When the ripple exceeds a critical value, the particle motion is shown to become stochastic through resonance overlapping mechanisms and collisionless diffusion occurs. Two regimes are clearly identified: in low ripple regions, the stochastic threshold is given by a standard Chirikov criterion, whereas in higher ripple zones, the motion is dominated by the perturbation structure around the resonances. Critical ripple values and diffusion coefficients are analytically determined in both regimes and the case of 3.5 MeV alpha particles in a reactor-sized tokamak such as ITER is discussed.
Bibliographic Reference: Report: EUR-CEA-FC-1382 EN (1989) 27 pp.
Availability: Available from CEA, Département de Recherches sur la Fusion Contrôlée, Saint-Paul-lez-Durance (FR)
Record Number: 199010734 / Last updated on: 1994-12-01
Original language: en
Available languages: en