Topology optimization of permanent magnets for stellarators

TL;DR

This paper presents a novel topology optimization method and the FAMUS code for designing permanent magnets in stellarators, enabling simplified coil configurations with high accuracy and plasma access.

Contribution

The paper introduces FAMUS, a new numerical tool for designing feasible permanent magnets in stellarators, verified against existing methods and demonstrated on a half-Tesla NCSX configuration.

Findings

FAMUS successfully designs magnets that generate desired equilibria.

Designed magnets provide large plasma access and high accuracy.

FAMUS is flexible and suitable for future stellarator designs.

Abstract

We introduce a topology optimization method to design permanent magnets for advanced stellarators. Recent researches show that permanent magnets have great potentials to simplify stellarator coils. We adopt state-of-the-art numerical techniques to determine the presence of magnets in the entire designing space. The FAMUS code is developed and it can design engineering-feasible permanent magnets for general stellarators satisfying the constraints of the maximum material magnetization and explicitly forbidden regions. FAMUS has been successfully verified against the previously proposed linear method. Three different permanent magnet designs together with planar TF coils for a half-Tesla NCSX configuration have been obtained for demonstrations. The designs have good accuracy in generating the desired equilibrium and offer considerably large plasma access on the outboard side. The results show that FAMUS is a flexible, advanced numerical tool for future permanent magnet stellarator designs.