Chaotic trajectories in tokamaks with magnetic islands and electrostatic waves
For over 20 years, it has been known that the overlapping of two chains of magnetic islands leads to field line stochasticity, i.e. magnetic braiding, and chaotic motion of the particles. This occurs in tokamaks as the result of two helical resonant perturbations, or of only one perturbation with toroidal effects. One major result in the study of non-linear systems is the onset of Lagrangian chaos in the particle motion, due to only a few regular modes. Similarly, chaotic motion is obtained for particles of guiding centres in the presence of a few electrostatic waves. The well-known paradigm system is given by a charged particle in two electrostatic waves; it is described by a non-autonomous Hamiltonian with 1(½) degree of freedom. For guiding centres, the motion becomes chaotic in the presence of three plane waves propagating in the plane perpendicular to the magnetic field. In the present work it is shown that the presence of a single electrostatic wave can trigger a chaotic diffusion of particles across a chain of magnetic islands. A mixed scenario is described where radial diffusion occurs in a tokamak from one magnetic chain to the other, even without any overlapping between magnetic islands, thus without any magnetic field line stochasticity. These results have been obtained in a sheared slab geometry. A full realistic description with toroidal drifts is also considered in order to test the validity of this mixed scenario of turbulent diffusion across different non-overlapping chains of magnetic islands.
Bibliographic Reference: Paper presented: Dynamics Days, Berlin (DE), June 12-15, 1991
Availability: Available from (1) as Paper EN 36153 ORA
Record Number: 199110765 / Last updated on: 1994-12-02
Original language: en
Available languages: en