Designing stellarators using perpendicular permanent magnets

TL;DR

This paper introduces a rapid design method for perpendicular permanent magnets to simplify stellarator coils, offering an alternative to electromagnetic coils for generating complex 3D magnetic fields in stellarator devices.

Contribution

The paper presents a novel, efficient approach to design permanent magnets for stellarators, demonstrating the feasibility of coil simplification using magnetic dipoles and an incremental multi-layer method.

Findings

Successfully reproduces a half-Tesla NCSX configuration with permanent magnets.

Proves surface magnetization is equivalent to surface current in coil design.

Shows stellarator coils can be substantially simplified with permanent magnets.

Abstract

We have developed a fast method to design perpendicular permanent magnets for simplifying stellarator coils based on existing codes. Coil complexity is one of the main challenges for stellarators. To date, only electromagnetic coils have been used to generate 3D fields for stellarators. Permanent magnets provide an alternative way to produce the desired magnetic field for optimized stellarators. In this paper, we revisit the concept of representing surface current using magnetic dipoles and carry out numerical validations. A surface magnetization is proven to be equivalent to the surface current that can be linearly solved by existing coil design codes. An incremental multi-layer method has been developed to obtain a practical solution that is attainable with present permanent magnets. With this method, we can reproduce a half-Tesla NCSX configuration using specially designed neodymium magnets together with simple planar coils. It shows that stellarator coils could be substantially simplified by adopting permanent magnets.