SYMMETRICAL SIMPLE MAP FOR A SINGLE-NULL DIVERTOR TOKAMAK

A new map called the symmetric simple map is introduced to represent t he chaotic trajectories of magnetic field lines in the scrape-off laye r of a single-null divertor tokamak. Good surfaces of this map are ver y nearly axisymmetric. Therefore it gives a far better representation of the magnetic topology of a single-null divertor tokamak. The map is investigated in detail and used to analyze the generic features of th e field line trajectories and their footprint on the divertor plate. T he map is employed to calculate the variations in the fraction of magn etic flux from the stochastic layer diverted onto plate, in the footpr int and in related parameters as the map parameter is varied. The Lyap unov exponents and the field diffusion coefficients are calculated. Th e low mode number map and the dipole map are introduced to include the effects of low and high mode number perturbations in the new map. (C) 1997 American Institute of Physics.