On description of magnetic stochasticity in poloidal divertor tokamaks

A generic approach to study the stochastic field lines formed near the magnetic separatrix of poloidal divertor tokamaks due to nonaxisymmetric magnetic perturbations is proposed. The method is based on the determination of the so-called Poincare integral [S. S. Abdullaev, Phys. Rev. E 70, 046202 (2004)] defined as an integral over the vector potential of the perturbation field taken along the closed field lines orbit. This integral allows us to obtain the analytical estimations for the characteristics of chaotic field lines near the magnetic separatrix, like the Chirikov parameter, the widths of the stochastic layer and magnetic footprints, also the statistical characteristics of chaotic field lines, the quasilinear field line diffusion coefficients, and the Kolmogorov lengths. These estimations are in good agreement with the direct numerical calculations of corresponding quantities. A field line convection coefficient is introduced to describe the preferential outward drift of open chaotic field lines near the separatrix. (c) 2008 American Institute of Physics.