Initial evaluation of miniature ultra-high-field commercial stellarator reactors with breeding external to resistive coils

TL;DR

This paper evaluates a novel ultra-high-field, small-volume stellarator reactor design with external breeding, focusing on its feasibility, key parameters, and potential for net electricity production.

Contribution

It introduces a new concept of a pulsed, high-field stellarator with external breeding, addressing size limitations and system complexity for commercial fusion reactors.

Findings

Small plasma volume (~2-4 m^3) with ultra-high magnetic field (~10-20 T) is feasible.

Distributed Divertor effectively extracts heat power from ionized particles.

The reactor design shows potential for net electricity production under certain operating conditions.

Abstract

The working parameters and challenges of ultra-high-field pulsed commercial stellarator reactors of small plasma volume with breeding external to resistive coils ($transposed$ stellarator) are studied. They may allow production of commercial heat and electricity in a tiny and simple device, and contribute to the knowledge on burning plasmas. The concept is based on the previous works (V. Queral et al.) performed for the high-field experimental fusion reactor i-ASTER (J. Fus. Energy 37 2018) and the recent Distributed Divertor concept (non-resonant divertor on the full toroid; J. Fus. Energy 44 2025). The present proposal is driven by the limitation on the minimum size of typical commercial stellarator reactors (~ space for internal breeding/shielding of SC coils). This limit is about 400 $\text{m}^3$ plasma volume, as deduced from e.g. ARIES-CS, ASTER-CP-(IEEE Trans. Plasma Sci. 52 2024) and Stellaris reactors. This fact, together with the accuracy and complexity of the systems, hinders quick iterations for the fast development of stellarator reactors. The concept is based on a pulsed high-beta large-aspect-ratio stellarator of small plasma volume (2-4 $\text{m}^3$) and ultra-high magnetic field (~ 10-20 T), composed by an external monolithic coil support and internal resistive coils (alike i-ASTER and UST_3 stellarators) of high neutron transparency, thermally-adiabatic conductors, a low-recycling Distributed Divertor to extract the heat power from ionized particles (pulse length ~ 5 $\tau$E), low pulsed duty cycle of 1-5%, and liquid breeding material around and externally to the reactor core. Different cases and operating points are studied. The main elements, e.g. heat power on the Distributed Divertor, radiation lifetime, and the prospect of net electricity production are evaluated. The involved challenges, impacting the potential feasibility of the concept, are assessed.