Effects of dipole perturbation on the stochastic layer and magnetic footprint in single-null divertor tokamaks

摘要

In this paper, the method of maps is used to calculate the effects of high toroidal and poloidal mode number perturbation on the trajectories of magnetic field lines in a single-null divertor tokamak. First, a simplified derivation of the dipole map from the Hamiltonian mechanics of magnetic field is given. This map represents the effects of an externally located current carrying coil on the motion of field lines. The unperturbed magnetic field topology of a single-null divertor tokamak is represented by the symmetric simple map. The coil is placed across from the X-point on the line joining the X-point and the O-point at a fixed distance from the last good confining surface. The effects of coil on the stochastic layer and magnetic footprint are calculated using the symmetric simple map and the dipole map. Self-similarities, singularities, and topological equivalences in the pattern of physical parameters are found that characterize the stochastic layer and the magnetic footprint. The dipole perturbation increases the area of footprint, drastically reduces the fraction of heat flux escaping the stochastic layer, disperses the heat flux more evenly over a wider area, and reduces number of hotspots on the collector plate. (C) 2003 American Institute of Physics. [References: 25]