Nonresonant stellarator divertors

Nonresonant stellarator divertor is extremely important for the development of stellarator concept. In our study of the nonresonant stellarator divertor to date, we have found three distinct types of stellarator divertors: the nonresonant stellarator divertor, the hybrid stellarator divertor, and the two-mode stellarator divertor. The nonresonant stellarator divertor has no large islands outside the outermost surface; the hybrid divertor has a chain of large islands outside and near the outermost surface and it has features of both the island divertor and the nonresonant divertor; the two-mode divertor has chains of many very small islands outside and near the outermost surface. The key property of these stellarator divertors is that the field lines exiting and approaching the region just outside the outermost surface are collimated into magnetic turnstiles. The field lines cross the cantori just outside the outermost surface through the holes in the cantori collimating in the turnstiles. A turnstile always comes in a pair of an outgoing flux tube and incoming tube. Intersection of the tubes with the wall give the magnetic footprints. The two tubes of a turnstile can start at adjacent or separate locations outside the outermost surface. Pseudo-turnstiles can also exist. A turnstile is characterized by its probability exponent. The locations of the footprint on the wall are fixed and robust. We will present a comprehensive view of the progress made in our study of nonresonant stellarator divertors.