V. Tribaldos | Searcharxiv

arXiv2025

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

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.

physics.plasm-ph↗

arXiv2025

Coil geometry with large openings for a HSR3-like stellarator reactor for fast replacement of in-vessel components

Advanced stellarators require convoluted modular coils to produce a plasma with satisfactory performance. Moreover, the number of coils is sometimes high to decrease the modular ripple created by the coils. For reactor stellarators, these requirements imply relatively small ports for in-vessel access and maintenance, i.e. in comparison with tokamaks. The blankets and divertor modules will have to be replaced periodically (about each 1-4 years depending on the design) due to neutron damage, and also erosion of divertor targets. Blanket modules are activated, thus, all the maintenance operations have to be produced remotely. In order to reduce the shutdown time and cost during component replacement, and to reduce the number, speed and other specifications of the remote maintenance equipment, the number of blanket modules in the reactor should be low and thus, the blanket modules should be large (in relation to the minor and major radius). Nevertheless, the size of the openings between coils limits the maximum size of the blanket and divertor modules, though several potential enhancements have been proposed in the past for stellarators, like straightening the outboard segments of the coils and the movement and/or expansion of certain coils to have wider access. The present work reports on a coil geometry for the 'Helias Stellarator Reactor' (HSR) of three periods (HSR3) with coils located far from the plasma at the outboard region of the straight-like sector. This feature creates natural wide openings at such regions of the coils, which may be utilized to allow access to large blanket and divertor modules.

physics.plasm-ph↗