Effect of nonaxisymmetric perturbations on the structure of a tokamak poloidal divertor

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Abstract
The effects of n=1 nonaxisymmetric perturbations on a tokamak poloidal divertor are described. Despite the existence of a region of chaotic field line trajectories outside the last closed flux surface, the footprint of the trajectories on the divertor plates is found to be largely coherent, forming a spiral structure. At a fixed toroidal angle, the footprint exhibits a bifurcation similar to that seen experimentally on DIII‐D [Nucl. Fusion 2 8, 902 (1988)]. For field errors of the magnitude that exist in present‐day tokamaks, the width of the nonaxisymmetric structure in the divertor footprint is comparable to the width of the scrape‐off layer.