Optimization of stellarator configurations combining omnigenity and piecewise omnigenity

TL;DR

This paper introduces a novel optimization method for stellarator configurations that combines omnigenity and piecewise omnigenity, leading to configurations with improved neoclassical properties suitable for reactors.

Contribution

A new mapping technique within the exttt{OOPS} framework enables the creation of stellarator configurations that combine omnigenity and pwO, relaxing constraints while maintaining favorable properties.

Findings

Configurations exhibit good neoclassical transport

Compatible with magnetic well constraints

Potential for future stellarator reactors

Abstract

We present a method for optimizing stellarator configurations that combine omnigenity and piecewise omnigenity (pwO). Within the \texttt{OOPS} optimization framework [Liu \textit{et al.}, arXiv:2502.09350 (2025)], we introduce a mapping technique that can ``squeeze'' general omnigenous fields to approximate pwO in the high-field side. Using this approach, we obtain a range of optimized configurations that combine poloidal omnigenity (PO) and pwO, spanning different field periods and aspect ratios. We further show that these configurations are compatible with a magnetic well. The resulting configurations exhibit favorable neoclassical transport and bootstrap current properties while partially relaxing the strict constraints of omnigenity. These results suggest that such configurations are promising candidates for future stellarator reactors.