Geometric concepts for stellarator permanent magnet arrays

TL;DR

This paper investigates geometric concepts for designing permanent magnet arrays in stellarators, using simulations to determine configurations that meet magnetic field requirements within physical magnet constraints.

Contribution

It introduces a study of magnet array geometries using the MAGPIE code, exploring configurations that satisfy stellarator magnetic field needs considering polarization constraints.

Findings

Constrained polarization configurations cannot meet magnetic requirements with current magnet strengths.

Unconstrained polarization configurations can satisfy the magnetic field requirements.

Geometric concepts for magnet arrays are validated using a test case similar to NCSX.

Abstract

The development of stellarators that use permanent magnet arrays to shape their confining magnetic fields has been a topic of recent interest, but the requirements for how such magnets must be shaped, manufactured, and assembled remain to be determined. To address these open questions, we have performed a study of geometric concepts for magnet arrays with the aid of the newly developed MAGPIE code. A proposed experiment similar to the National Compact Stellarator Experiment (NCSX) is used as a test case. Two classes of magnet geometry are explored: curved bricks that conform to a regular grid in cylindrical coordinates, and hexahedra that conform to the toroidal plasma geometry. In addition, we test constraints on the magnet polarization. While magnet configurations constrained to be polarized normally to a toroidal surface around the plasma are unable to meet the required magnetic field parameters when subject to physical limitations on the strength of present-day magnets, configurations with unconstrained polarizations are shown to satisfy the physics requirements for a targeted plasma.