Generic configuration stellarator based on several concentric Fourier windings

TL;DR

This paper introduces a systematic method to design modular, concentric Fourier winding coils for stellarators, enabling a broad variety of magnetic configurations to study their effects on plasma behavior.

Contribution

The paper presents a novel approach to generate multiple magnetic configurations in stellarators using concentric Fourier windings, expanding the design flexibility beyond traditional coil sets.

Findings

Method successfully generates diverse magnetic configurations.

Modelled LCFS closely matches Poincaré plots from magnetic field combinations.

Application demonstrates the method's potential for stellarator design flexibility.

Abstract

Stellarators commonly comprise different sets of coils to produce diverse magnetic configurations. However, the diversity of possible configurations in a single device is usually rather limited. The achievement of a broad variety of magnetic configurations might be valuable for some purposes, for example, to assay the effect of the magnetic configuration on turbulent transport. Thus, a method is created to systematically define sets of modular coils located on concentric toroidal winding surfaces. The method is based on the expression of a Last Closed Flux Surface (LCFS) by Fourier coefficients in cylindrical coordinates and consists in the definition of successive windings located on equidistant concentric winding surfaces, each winding such that produces a magnetic field which, when added to the magnetic field generated by a sole base winding that generates a base magnetic configuration, produces a magnetic configuration whose LCFS is defined by the Fourier coefficients of the base magnetic configuration plus only one new Fourier coefficient. The utilization of a diversity of currents in the different windings would give a linear combination of magnetic fields that reproduce the LCFS defined mathematically by the respective Fourier coefficients. The deviation between a particular modelled LCFS and the obtained LCFS from the windings depends on: the order and value of each Fourier coefficient, the selected shape of concentric winding surfaces, and the possible intersection of the LCFS with the internal winding surface. The method to generate the windings is reported and the application to one case study is described. Each modelled LCFS is compared with the respective Poincar\'e plot obtained from the linear combination of magnetic fields from the windings.