Widening the magnetic footprints in a poloidal divertor tokamak: A proposal

A dynamic ergodization for the control of heat deposition on divertor plates in a poloidal divertor tokamak is proposed. A weak ergodization of magnetic field lines near the magnetic separatrix by external rotating magnetic field perturbations is considered. The analysis of perturbed field lines is carried out using the computationally efficient method of the shifted separatrix mapping. The structure of the stochastic layer of open field lines near the X point and of the magnetic footprints on the divertor plates is studied for different harmonics of the magnetic perturbations. The perturbation field generates both an ergodic widening of the divertor footprints and a laminar deformation, which is averaged out by the proposed rotation of the perturbation field. Some technical implications of the application of such a perturbation field for the Next Step Device are discussed.