A symplectic mapping for the ergodic magnetic limiter and its dynamical analysis

A model for a new bidimensional sympletic mapping describing magnetic field line trajectories in a tokamak perturbed by ergodic magnetic limiter coils is presented. Numerical examples of these trajectories, computed for plasm a described by large aspect-ratio equilibria, simulate the main characteris tics of trajectories in the toroidal geometry. Also the importance of the s ymplecticity of the new mapping regarding certain features of non-linear dy namical analysis, for which a large number of iterations is necessary, is s hown. Thus, some standard algorithms, such as the Lyapunov exponents and th e rotational transforms, are applied with precision in order to characteriz e regular and chaotic regions in the parameter space, improving the study o f bifurcations, routes to chaos, and diffusion in this system. (C) 2000 Els evier Science Ltd. All rights reserved.