Magnetic turnstiles of a new type of stellarator divertor – the hybrid stellarator divertor

A new type of stellarator divertor is discovered. It has properties of both the island divertor and the nonresonant divertor. For this reason, we have called it hybrid divertor. This new divertor has some desirable properties [see http://meetings.aps.org/Meeting/DPP20/Session/BP14.18] which are of practical value. The field lines from just outside the outermost confining magnetic surface reach the wall through magnetic turnstiles. Magnetic turnstiles always come in a pair of magnetic flux tubes – an outgoing flux tube and an incoming flux tube. This is because magnetic field is divergence-free. The outgoing flux tube carries magnetic flux from just outside the outermost surface, and the incoming tube carries the flux from the wall to just outside the outermost surface. We have calculated the full 3D magnetic turnstiles of the hybrid divertor using the method developed in [A. Punjabi and A. H. Boozer, Phys. Plasmas 29, 012502 (2022)]. We have found that there are three magnetic turnstiles in hybrid divertor. All three are adjoining turnstiles. This means that the magnetic flux tubes of each of these three turnstiles start at adjoining locations just outside the outermost surface. We have also calculated the probability exponents of these three magnetic turnstiles in hybrid divertor using the method developed in [A. H. Boozer and A. Punjabi, Phys Plasmas 25, 092505 (2018); A. Punjabi and A. H. Boozer, Phys. Plasmas 27, 012503 (2020) (Editors Pick)]. We have found that the probability exponents are 2.21, 2.25, and 4.43]. This work is supported by DOE OFES grants DE-SC0020107 to Hampton University, and DE-FG02-03ER54696 to Columbia University. Research used resources of the NERSC, supported by the Office of Science, US DOE, under Contract No. DE-AC02-05CH11231.