Magnetic field line mappings for a tokamak with ergodic limiters

An ergodic magnetic limiter is a device whose main effect in a tokamak is to create a cold boundary layer of chaotic magnetic field lines. In order to study its effect we have used two approaches. The first is a description of magnetic island formation through an analytical method to describe its dimensions, results being in accordance with numerical Poincaré maps for magnetic field lines. The second is a model which simulates the ergodic limiter action as a sequence of impulsive perturbations, enabling the derivation of analytical formulae for the Poincaré maps.