AbstractResonant perturbations of sufficient amplitude impose an ergodic structure on the field line trajectories. In the standard theory, these features are related to the amplitude of the resonant Fourier components of the Br-field. The characteristic parameters of an ergodized field are the width of magnetic islands, the Chirikov parameter (amount of overlapping of islands) and the coherence length (Kolmogorov length). The perturbation current amplitude allows for Chirikov parameters of up to 1.6 for the pure 12/4 excitation mode. The Chirikov value is very sensitive to a possible mixing of 12/4 and 6/2 modes and can considerably be enhanced.