Robustness of stellarator divertors to coil perturbations

Determine whether a stellarator divertor configuration can be realized whose separatrix and diverted field-line topology remain intact under small perturbations of the modular coil geometry, i.e., a divertor robust to coil perturbations.

Background

The paper introduces coil optimization methods (including weighted squared flux and manifold optimization) to realize a helical divertor topology with sharp X-lines using modular coils. While separatrix chaos can be reduced, the manifold-optimized configuration exhibits extreme sensitivity to small coil changes, reflecting the fragility of separatrices when diverted field lines pass close to diverting coils.

This sensitivity complicates computational design and suggests a fundamental challenge: ensuring that the cleaned separatrix and diverted topology persist under realistic manufacturing tolerances or operational perturbations. The authors explicitly state that it remains to be shown whether a divertor robust to such perturbations can be realized.