Robust stellarator optimization via flat mirror magnetic fields

TL;DR

This paper demonstrates that flat-mirror quasi-isodynamic stellarator configurations can achieve good confinement and robustness, simplifying design and operation of fusion reactors even without perfect omnigeneity.

Contribution

It introduces flat-mirror quasi-isodynamic configurations as a robust alternative to traditional stellarator designs, enhancing ease of construction and operation.

Findings

Small radial transport achieved despite deviations from perfect omnigeneity

Configurations are robust against error fields and various plasma scenarios

Reduced fast ion losses improve plasma-facing component longevity

Abstract

Stellarator magnetic configurations need to be optimized in order to meet all the required properties of a fusion reactor. In this work, it is shown that a flat-mirror quasi-isodynamic configuration (i.e. a quasi-isodynamic configuration with sufficiently small radial variation of the mirror term) can achieve small radial transport of energy and good confinement of bulk and fast ions even if it is not very close to perfect omnigeneity, and for a wide range of plasma scenarios, including low $\beta$ and small radial electric field. This opens the door to constructing better stellarator reactors. On the one hand, they would be easier to design, as they would be robust against error fields. On the other hand, they would be easier to operate since, both during startup and steady-state operation, they would require less auxiliary power, and the damage to plasma-facing components caused by fast ion losses would be reduced to acceptable levels.