MOTION IN A STOCHASTIC LAYER DESCRIBED BY SYMBOLIC DYNAMICS

The motion in the stochastic layer surrounding an island can be studie d by using the standard map: This problem is of direct relevance to th e diffusion of magnetic field lines in a tokamak. In a previous work i t was shown that this process can be adequately modelled by a continuo us time random walk (CTRW) describing transitions of the running point between three basins representing, respectively, trapped motion aroun d the island, and passing motion above or below the island. The sticki ng property of the island deeply modifies the nature of the transport process, leading to subdiffusive behavior. In the present work it is s hown that the motion can be analyzed in terms of a symbolic dynamics w hich leads to the possibility of an automatic measurement of the data necessary for the construction of the CTRW. The logical features of th e 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.