Magnetic turnstiles in nonresonant stellarator divertor

TL;DR

This paper investigates magnetic flux tube behaviors called turnstiles and pseudo turnstiles in nonresonant stellarator divertors, revealing complex crossing and exit patterns that improve understanding of plasma confinement and divertor design.

Contribution

It introduces the concept of pseudo turnstiles and details their formation and implications, expanding the understanding of magnetic flux tube dynamics in stellarator divertors.

Findings

Existence of non-adjacent and adjacent turnstiles and pseudo turnstiles.

Pseudo turnstiles form when a cantorus strikes the chamber wall.

Clarifies previous simulation issues in stellarator divertors.

Abstract

Non-resonant stellarator divertors have magnetic flux tubes, called magnetic turnstiles, that cross cantori, which are fractal remnants of destroyed invariant tori with holes, that lie outside the outermost confining surface. The exiting and entering flux tubes can be adjacent as is generally expected but can also have the unexpected feature of entering or exiting at separate locations of the cantori. Not only can there be two types of turnstiles, but pseudo turnstiles can also exist. A pseudo turnstile is formed when a cantorus has a sufficiently large, although limited, radial excursion to strike a surrounding chamber wall. The existence of non-adjacent and adjacent turnstiles and pseudo turnstiles resolves issues that arose in earlier simulations of nonresonant stellarator divertors [A. Punjabi and A. H. Boozer, Phys. Plasmas 27, 012503 (2020)].