Simulation of non-resonant stellarator divertor

TL;DR

This paper applies an efficient numerical method to study nonresonant stellarator divertors, revealing distinct behaviors of diffusive magnetic field lines and their exit patterns, with implications for magnetic confinement and wall design.

Contribution

It introduces a novel analysis of diffusive magnetic field lines in nonresonant stellarator divertors, identifying their exit patterns and probabilities, and addresses previous numerical limitations.

Findings

Diffusive lines exit only through the primary turnstile below a certain velocity.

Footprints of line families are symmetric and fixed on the wall.

Probability exponents for turnstile exit pathways are d1=9/4 and d2=3/2.

Abstract

An efficient numerical method of studying nonresonant stellarator divertors was introduced in Boozer and Punjabi [Phys. Plasmas 25, 092505 (2018)]. This method is used in this paper to study a different magnetic field model of a nonresonant divertor. The most novel and interesting finding of this study is that diffusive magnetic field lines can be distinguished from lines that exit through the primary and the secondary turnstile, and that below some diffusive velocity, all lines exit through only the primary turnstile. The footprints of each family are stellarator symmetric and have a fixed location on the wall for all velocities. The probability exponent of the primary turnstile is d1 = 9/4 and that of the secondary turnstile is d2 = 3/2. This study also addresses the issues of an inadequate separation of the chamber walls from the outermost confining magnetic surface and a marginal step size of the numerical integrations that could compromise the interpretation of the earlier results [Boozer and Punjabi, Phys. Plasmas 25, 092505 (2018)]. The previous value of d1 = 2 is within the error bar of d1 = 9/4 estimated here.