LNF:(2022-2026) Estudio de ensamblajes mejorados para stellarator congruentes con componentes in-vessel innovadores para lograr reactores viables de alto campo

LNF - Nationally funded project

Title: Estudio de ensamblajes mejorados para stellarator congruentes con componentes in-vessel innovadores para lograr reactores viables de alto campo

Reference: PID2021-123616OB-I00

Programme and date: Plan Estatal de Investigación Científica, Técnica y de Innovación 2021-2023

Programme type (Modalidad de proyecto): Investigación Orientada

Area/subarea (Área temática / subárea): Prioridad temática: Clima, Energía y Movilidad ; Principal: Ciencias físicas / Secundaria: Producción industrial, ingeniería civil e ingenierías para la sociedad

Principal Investigator(s): Vicente Manuel Queral Mas [1] , Mª Esther Rincón Rincón [2]

Project type: Proyecto individual

Start-end dates: 01/09/2022 - 31/05/2026

Financing granted (direct costs): 39.200 €

Acknowledgement: Grant PID2021-123616OB-I00 financiado por MICIU/AEI/ 10.13039/501100011033 y por “FEDER/EU”.

Description of the project

The project proposes the integrative study of stellarator structural arrangements of appropriate geometry, which will allow innovative in-vessel components (geometrically simplified, more easily manufacturable, high-power) in order to achieve coherent and feasible high-field stellarator reactors. Thus, obtaining more commercially attractive fusion reactor designs for energy production. The term 'Structural arrangements' includes: the distribution and size of openings for in-vessel access, coil distribution and the geometry of their mechanical supports, and the location of in-vessel components (IVCs). It is known that the power of a future fusion reactor will scale as the fourth power of the magnetic field, enabling high fusion power density and more attractive reactors. Certainly, high-field tokamak experiments exist and reactors were designed (i.e. Alcator line; ARC 2015), while for stellarators it is a relatively recent line (AIS & i-ASTER stellarators, Queral 2010/18). Despite the advantages, high power (surface) density originates three essential problems: rapid neutron damage of the IVCs (activated and requiring replacement and storage), more frequent remote maintenance of IVCs (~downtime), and difficult power extraction. The previous works on stellarator structures (i.e. Queral Rincón, IEEE Trans. Plasma Sci. 48 2020), coil distributions (i.e. UST_1 Queral Fus. Eng. Des., F.E.D., 2016), high-field ignition reactors (i.e. Queral, J. of Fus. Energy 37 2018) and advanced manufacturing (several publications), performed in the State Plans of R&D 2015 and 2018; and other works performed by the research team on IVCs (i.e. Fernández F.E.D. 155 2020), liquid metals for first-wall (de Castro 2021), tokamak design (i.e. JT-60SA Rincón F.E.D. 2011) and on remote maintenance (DEMO, ITER, IFMIF), together with earlier research in the fields, are the starting point to realistically undertake the study. In relation to such problems, opportunities and background, the project conjectures whether an appropriate structural arrangement of stellarator may open the door to more satisfactory IVCs, and pursues the objectives: i) study and conceptual design of improved stellarator structural arrangements, comprising: A) finding improved coil distributions to have adequate openings for simple and fast replacement of IVCs, and simultaneously to open the door to geometrically simplified IVCs, B) investigating geometrically simplified IVCs and proper materials for easier advanced manufacturing of IVCs, which is critical due to their frequent replacement, and, C) selection of a proper high-power system for the first-wall of the IVC, ii) experimental validation of the selected best arrangement by manufacturing tests (advanced casting or additive manufacturing) of a scaled-down sector of the simplified IVC and the surrounding components. The results of the project will contribute to the European Fusion Program, which aims at bringing the stellarator line to maturity, expand an almost unexplored research field, importantly contribute to advance faster towards a powerful dispatchable energy system for the society needs, and also generate applications external to the fusion field, like advanced fabrication of large metallic components.

Main results

The project investigated, in an integrated manner, stellarator structural arrangements incorporating geometries specifically designed to accommodate innovative in-vessel components (IVCs), with the aim of achieving feasible and commercially attractive high-field stellarator reactors. High magnetic fields lead to high power density, which, although beneficial because it increases power output, also results in greater neutron damage to IVCs, more frequent and complex remote maintenance, and more challenging heat extraction. To mitigate these problems, three novel structural arrangements were developed. The first reactor/arrangement concept eliminates solid IVCs by replacing them with liquids, which are not damaged by neutron irradiation and therefore require neither replacement nor maintenance. This concept integrates an innovative magnetic configuration with a structural arrangement consisting of cylinders with centrifugally confined peripheral liquid. Experimental tests and finite-element analyses (FEA) of centrifugal water flows were carried out for validation, yielding satisfactory results. The concept and the corresponding results were published in ‘On a High-Mirror Stellarator Reactor Energy Concept With Neutrons Concentrated on Centrifuge Liquids’, IEEE Transactions on Plasma Science 52 (2024) 3731. The second reactor/arrangement concept employs centrifugally confined in-vessel liquids throughout the entire toroidal vacuum chamber by means of smoothly rounded (rather than cylindrical) vacuum vessel geometries. Experimental investigations were performed using centrifugal liquid metal (Galinstan) under magnetic fields, centrifugal water flow in a 3D-printed toroidal vessel, and static lithium floating on molten lithium salt. In addition, a new divertor concept, the Distributed Divertor, was invented to distribute the ionized particle flux. The concepts and experimental results were published in ‘Li Divertor Targets and Walls for the ASTER Liquid Stellarator Reactor, Distributed Divertor’, Journal of Fusion Energy 44 (2025) 15, and were also protected by the Spanish patent P202430653. The third innovative reactor/layout concept places the tritium breeding material outside resistive (copper) coils, thereby eliminating in-vessel components altogether. Consequently, there is no need for neutron shielding of superconducting coils or internal breeding blankets. This arrangement makes it possible to reduce the plasma volume dramatically, to approximately 2–4 m³. The reactor core (coils and their structural support) must remain relatively thin (less than 0.3 m) to ensure an adequate tritium breeding ratio. The concept, together with calculations and estimates of all the principal reactor parameters, has been published as a preprint: ‘Initial Evaluation of Miniature Ultra-High-Field Commercial Stellarator Reactors with Breeding External to Resistive Coils’, arXiv, https://doi.org/10.48550/arXiv.2505.23485, version 2 (27 pp.), 2026. The results of the project contribute to the thematic priority ‘Climate, Energy and Mobility’, as they may accelerate the development of commercially viable fusion energy for society, thereby helping to avoid CO₂ emissions. They also contribute to the European Fusion Programme by exploring the stellarator as an alternative magnetic-confinement fusion concept.

Dissemination of project results (peer-reviewed publications and conference presentations)

PEER-REVIEWED ARTICLES IN THIS PROJECT

1. V. Queral, I. Fernández, A. de Castro, D. Spong, S. Cabrera, V. Tribaldos, J.M. Reynolds, E. Rincon, On a High-Mirror Stellarator Reactor Exploratory Concept With Neutrons Concentrated on Centrifuge Liquids, IEEE Transactions on Plasma Science 52 (2024) 3731-3737. https://doi.org/10.1109/TPS.2024.3350985

2. V. Queral, A. de Castro, J. Varela, S. Cabrera, I. Fernández, D. Spong, E. Rincón, Lithium Divertor Targets and Walls for the ASTER Liquid Stellarator reactor, Distributed Divertor, J. Fusion Energy 44 (2025) 15 (15pp) https://doi.org/10.1007/s10894-025-00481-8

NON-PEER-REVIEWED ARTICLES IN THIS PROJECT

1. 2. V. Queral, E. Rincon, A. de Castro, I. Fernandez-Berceruelo, I. Palermo, A. Moroño, V. Tribaldos, J.M. Reynolds, D. Spong, S. Cabrera, J. Varela, Initial evaluation of miniature ultra-high-field commercial stellarator reactors with breeding external to resistive coils, arXiv, https://doi.org/10.48550/arXiv.2505.23485 , versión 1 2025 (19pp), versión 2 2026 (27pp)-(Pre-print, enviado para su publicación en Fus. Eng. Des.)

3. V. Queral, I. Fernández, A. de Castro, D. Spong, S. Cabrera, V. Tribaldos, J.M. Reynolds, E. Rincon, F. Tabarés, Concept of a stellarator fusion reactor based on centrifuge molten salts in cylinders, Proceedings de la RA-SNE – 48, 2023. [3] , o buscar en [4]

4. V. Queral, V. Tribaldos, J.M. Reynolds, I. Fernandez, Coil geometry with large openings for a HSR3-like stellarator reactor for fast replacement of in-vessel components, Arxiv https://doi.org/10.48550/arXiv.2501.04640 (2025) (8pp)

POSTERS AND TALKS IN CONFERENCES IN THIS PROJECT

1. V. Queral, A. de Castro, I. Fernández-Berceruelo, D. Spong, J. Varela, E. Rincón, S. Cabrera, V. Tribaldos and J.M. Reynolds, Prospects of ‘Liquid Stellarator Reactors’ for enhanced competitiveness, POSTER contribution, 2025 Symposium On Fusion Engineering (SOFE), Cambridge (USA), 23–26 June 2025.

2. V. Queral, A. de Castro, J. Varela (U. of Texas, Austin, USA), S. Cabrera, I. Fernández, D. Spong (ORNL, USA), E. Rincón ; Roberto Suárez, Andrea Morilla (AST-Ingeniería), Li divertor targets and walls for the ASTER Liquid Stellarator reactor, ORAL contribution, 8th international Symposium on Liquid Metals Applications for Fusion (ISLA), Hefei (China), 08–12 September 2024.

3. V. Queral, I. Fernández, A. de Castro, D. Spong, S. Cabrera, V. Tribaldos, J.M. Reynolds, E. Rincon, F. Tabarés, Concepto de reactor de fusión stellarator basado en sales fundidas centrífugas dentro de cilindros, ORAL contribution, 48ª Reunión Anual de la Sociedad Nuclear Española, Toledo (Spain), 4–6 October 2023.

4. V. Queral, I. Fernández, A. de Castro, D. Spong, S. Cabrera, V. Tribaldos, J.M. Reynolds, E. Rincon, F. Tabarés, High mirror stellarator reactor concept with neutrons concentrated on centrifuge liquids, POSTER contribution, 30th Symposium On Fusion Engineering (SOFE), Oxford, (UK), 10–13 July 2023.

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