Magnetic field topology and field lines structure in the Dynamic Ergodic Divertor of TEXTOR-94

An analytical model of the magnetic field perturbations and the mapping technique to study field line dynamics in an ergodic divertor tokamak are developed. The analytical formulas for the vacuum magnetic field perturbations of ideal divertor coil configuration are derived. The Hamiltonian representation in toroidal geometry is discussed, and asymptotic formulas for it are found. The so-called symmetric perturbed twist mapping is derived and applied to the formation of a stochastic layer and statistical properties of field lines at the plasma edge.