ABSTRACT
The motion in the stochastic layer surrounding an island can be studied by using the standard map: This problem is of direct relevance to the diffusion of magnetic field lines in a tokamak. In a previous work it was shown that this process can be adequately modelled by a continuous time random walk (CTRW) describing transitions of the running point between three basins representing, respectively, trapped motion around the island, and passing motion above or below the island. The sticking property of the island deeply modifies the nature of the transport process, leading to subdiffusive behavior. In the present work it is shown that the motion can be analyzed in terms of a symbolic dynamics which leads to the possibility of an automatic measurement of the data necessary for the construction of the CTRW. The logical features of the procedure are described, and the method is applied to an analysis of long time series, thus completing the results of the previous work. (c) 1998 American Institute of Physics.
