Design of an arrangement of cubic magnets for a quasi-axisymmetric stellarator experiment

TL;DR

This paper presents a method for designing an array of cubic permanent magnets to shape magnetic fields in a stellarator, aiming to reduce reliance on complex coils for plasma confinement.

Contribution

It introduces a systematic design procedure for cubic permanent magnet arrays that work with toroidal coils to confine plasma in a stellarator, emphasizing fabrication simplicity.

Findings

Magnetic field confinement achieved with permanent magnets and coils.

Design method for magnet arrangement and polarization optimization.

Potential reduction in coil complexity for stellarator devices.

Abstract

The usage of permanent magnets to shape the confining magnetic field of a stellarator has the potential to reduce or eliminate the need for non-planar coils. As a proof-of-concept for this idea, we have developed a procedure for designing an array of cubic permanent magnets that works in tandem with a set of toroidal-field coils to confine a stellarator plasma. All of the magnets in the design are constrained to have identical geometry and one of three polarization types in order to simplify fabrication while still producing sufficient field accuracy. We present some of the key steps leading to the design, including the geometric arrangement of the magnets around the device, the procedure for optimizing the polarizations according to the three allowable magnet types, and the choice of magnet types to be used. We apply these methods to design an array of rare-Earth permanent magnets that can be paired with a set of planar toroidal-field coils to confine a quasi-axisymmetric plasma with a toroidal magnetic field strength of about 0.5 T on axis.