Thèse un Nouveau Concept de Source d'Ions Négatifs pour la Fusion par Confinement Magnétique - Vers une Énergie Électrique et des Technologies Industrielles Plus Propres H/F Doctorat.Gouv.Fr

Établissement : Université de Toulouse École doctorale : GEETS - Génie Electrique Electronique,Télécommunications et Santé : du système au nanosystème Laboratoire de recherche : LAPLACE - Laboratoire PLAsma et Conversion d'Énergie Direction de la thèse : Freddy GABORIAU ORCID 0000000187559744 Début de la thèse : 2026-10-01 Date limite de candidature : 2026-11-23T23:59:59 Ce projet de thèse porte sur un verrou technologique critique du système d'injection de neutres d'ITER : la source d'ions négatifs. Chauffer le plasma d'ITER nécessite des faisceaux de particules neutres à haute énergie, produits en générant puis en extrayant des ions négatifs avant de les neutraliser. Cette source n'est donc pas un composant périphérique, mais une technologie dont dépend directement la capacité d'ITER à atteindre et maintenir les conditions de fusion.

Le concept de référence, développé à l'IPP Garching (Allemagne), souffre de deux limitations majeures : une configuration de champ magnétique dipolaire génère un courant de Hall parasite, produisant une distribution de plasma asymétrique ; et à basse pression, un potentiel plasma excessivement élevé génère des neutres rapides par recombinaison, dégradant la divergence du faisceau dans l'accélérateur. Ces problèmes menacent la fiabilité de la chaîne de chauffage d'ITER et, plus largement, la maturité des sources d'ions négatifs comme brique des futures centrales à fusion.

Pour lever ces verrous, LAPLACE a développé un nouveau concept de source qui modifie la cartographie du champ magnétique afin de supprimer la dérive électronique responsable de l'effet Hall, restaurant l'axisymétrie du plasma, et de contrôler le potentiel plasma via des électrodes placées aux miroirs magnétiques. Des simulations 3D Particle-In-Cell confirment déjà des profils électroniques axisymétriques pour cette configuration. Un prototype aux dimensions industrielles est en cours de construction à LAPLACE et sera opérationnel en juillet 2026 ; une source à plus grande échelle, compatible avec l'injecteur d'ITER, sera construite au cours de la thèse.

La thèse comporte quatre objectifs : (1) démontrer expérimentalement l'axisymétrie du plasma ; (2) contrôler et réduire le potentiel plasma vers des valeurs comparables aux sources à filament ; (3) installer un extracteur d'ions négatifs et caractériser le faisceau extrait d'une seule ouverture ; (4) évaluer la faisabilité d'intégrer la source sur le banc d'essai de Padoue (Italie). Cette combinaison de travail expérimental et de modélisation 3D PIC offre une formation interdisciplinaire couvrant physique des plasmas, diagnostics, simulation numérique et ingénierie d'extraction de faisceaux.

Le projet est financé par le programme européen Eurofusion « Enabling Research » (270 K€), dans le cadre d'une nouvelle collaboration entre LAPLACE et le Consorzio RFX de Padoue, qui exploite la Neutral Beam Test Facility et est responsable du développement de l'injecteur de neutres d'ITER. Emanuele Sartori (maître de conférences, Université de Padoue), spécialiste de l'intégration des modules d'injecteurs, co-encadrera la thèse : il dirigera l'étude de faisabilité d'intégration à RFX (objectif 4) et contribuera à la conception de l'extracteur et à la caractérisation du faisceau (objectif 3).

Le doctorant sera principalement basé à LAPLACE (Toulouse), avec des séjours à RFX de Padoue totalisant quatre mois, financés par le projet Eurofusion. Cette mobilité internationale intégrée entre deux grands centres européens de fusion s'inscrit pleinement dans l'ambition de BEST de former des doctorants dans des cadres véritablement internationaux et interdisciplinaires, sur des questions de transition énergétique pertinentes pour la fusion et l'industrie.

Au-delà de sa contribution à l'injection de neutres d'ITER - technologie centrale pour la transition énergétique mondiale - ce travail devrait générer un savoir-faire transférable pour les sources d'ions négatifs dans le médical, le traitement de surface et la microélectronique, secteurs relevant du thème « industries du futur » de BEST. CONTEXT AND SOCIETAL CHALLENGE
Decarbonizing the world's energy supply while meeting rapidly growing electricity demand is one of the defining challenges of this century. Nuclear fusion offers a uniquely attractive answer: a virtually inexhaustible fuel source, no long-lived radioactive waste, and no risk of runaway reaction, making it a cornerstone candidate for the energy mix of the second half of the century. ITER, the largest international scientific collaboration ever built for energy research, exists precisely to prove that fusion power can be delivered at an industrial scale - and its success depends on solving a number of hard engineering and plasma-physics bottlenecks that remain unresolved today. This thesis addresses one of them.
Heating the ITER plasma to fusion-relevant temperatures requires injecting high-energy neutral particle beams, produced by first generating and extracting negative ions and then neutralizing them. The source that generates these negative ions is therefore not a peripheral component but a technology on which the entire heating strategy - and hence ITER's ability to reach and sustain fusion conditions - directly depends. The source concept currently developed at IPP Garching (Germany) still suffers from two major limitations that threaten the reliability and efficiency of this heating chain: an asymmetric plasma distribution caused by a dipolar magnetic field configuration that drives a parasitic Hall current, and, at low operating pressure (0.3 Pa), an excessively high plasma potential (~70 V) that generates fast neutrals through recombination, degrading the beam divergence in the accelerator (angular acceptance below 10³ over 1280 individual beamlets) [1]. Removing these bottlenecks is a precondition for ITER's neutral beam system to perform as designed, and, more broadly, for negative-ion-source technology to mature into a reliable building block of future fusion power plants.
The societal relevance of this work extends beyond fusion itself. The same source technology, once made more compact, symmetric, and energy-efficient, is directly transferable to medical industry, surface treatment, and microelectronics - sectors themselves engaged in their own transitions towards cleaner, more precise, and more resource-efficient processes. This PhD project therefore sits at the intersection of two transitions: the long-term energy transition embodied by fusion research, and the shorter-term industrial transition towards greener plasma-based manufacturing technologies, giving the doctoral candidate the opportunity to develop expertise with impact on both fronts.

SCIENTIFIC BACKGROUND
Fusion-relevant negative-ion sources rely on an inductively-coupled RF discharge combined with a magnetized expansion region that reduces the electron flux and temperature near the extraction zone. In the reference ITER concept (BATMAN Upgrade source), the plasma asymmetry originates from an electron drift towards the lateral walls, which generates a transverse electric field to preserve quasi-neutrality [2], [3].

PROPOSED INNOVATION
The new source concept proposed by LAPLACE modifies the magnetic field mapping to: (i) suppress the electron drift (cancelling the Hall effect) and restore plasma axisymmetry; (ii) control the amplitude and profile of the plasma potential using electrodes placed at the magnetic mirrors [4]. Three-dimensional Particle-In-Cell (PIC) simulations confirm axisymmetric electron temperature profiles for this configuration. A source of dimensions compatible with industrial applications is currently being designed at LAPLACE and will be operational in July 2026; a larger-scale source compatible with the ITER neutral beam injector will be built during the course of the thesis.

PHD OBJECTIVES
1. Experimentally demonstrate the plasma axisymmetry of the new source concept.
2. Control and reduce the plasma potential towards values comparable to filament-based sources.
3. Install a negative-ion extractor on the LAPLACE source and characterise the extracted negative-ion beam from a single aperture.
4. Assess the feasibility of integrating the new source into the test bench located in Padova (Italy).
The project combines experimental work with 3D PIC modelling, giving the doctoral candidate a genuinely interdisciplinary training spanning plasma physics, diagnostics, numerical simulation, and beam extraction engineering.

INTERNATIONAL AND INTERSECTORAL DIMENSION
This project is funded by the European Eurofusion 'Enabling Research' program, in a new collaboration between LAPLACE and Consorzio RFX (Padova, Italy), which operates the Neutral Beam Test Facility (NBTF) and is responsible for developing ITER's neutral beam injector. Funding of €270k covers equipment, researcher time, and mission costs. Emanuele Sartori (Assistant Professor, University of Padova), specialist in the integration of neutral-beam-injector modules, will co-supervise the thesis and lead, together with his team, the feasibility study for integrating the LAPLACE source at RFX (objective 4), while also contributing actively to the extractor design and beam characterization (objective 3).
The doctoral candidate will be based mainly at LAPLACE (Toulouse) with planned secondments to RFX in Padova (four months in total over the course of the thesis), funded by the Eurofusion project. This built-in international mobility between two European fusion research centers directly aligns with BEST's ambition to train doctoral researchers within genuinely international and interdisciplinary settings, on questions of energy transition relevant to both fusion and industry.

EXPECTED IMPACT
Beyond its direct contribution to ITER's neutral beam injection system, a fusion energy technology central to the global energy transition, this work is expected to yield transferable know-how for negative-ion source design in medical technology, surface treatment, and microelectronics - sectors central to the 'industries of the future' theme of the BEST program.
1- Scientific/technological objective - Develop and experimentally validate a new negative-ion source concept that overcomes the two major limitations of the current ITER reference design: plasma asymmetry caused by a parasitic Hall current, and excessive plasma potential degrading beam quality at low operating pressure.
2- Engineering/integration objective - Move the new source concept from a laboratory prototype to a design compatible with negative-ion extraction and beam characterisation, and assess its feasibility for integration into the ITER-relevant test infrastructure at RFX (Padova).
3- Industrial transfer objective - Generate transferable know-how applicable beyond fusion, to industrial plasma-based technologies such as medical devices, surface treatment, and microelectronics, contributing to the broader industrial transition towards cleaner and more resource-efficient processes.
4- Training and mobility objective - Provide the doctoral candidate with a genuinely interdisciplinary and international training experience, combining experimental plasma physics, 3D PIC modelling, and beam extraction engineering, through a structured collaboration and mobility scheme between LAPLACE (Toulouse) and Consorzio RFX (Padova). The project combines experimental plasma physics with numerical modelling, structured around the four PhD objectives.

Experimental approach. Work will be carried out on the new negative-ion source prototype currently being built at LAPLACE, and on a larger-scale source to be constructed during the thesis for compatibility with the ITER neutral beam injector. Plasma diagnostics (Langmuir probes, optical emission spectroscopy, and dedicated potential measurements) will be used to experimentally map plasma symmetry and quantify the plasma potential under the new magnetic field configuration, and to compare these results with the reference (dipolar) configuration.

Numerical modelling. Three-dimensional Particle-In-Cell (PIC) simulations, already used to predict the axisymmetric electron temperature profiles of the new concept, will continue to guide the interpretation of experimental results and to optimise the magnetic mirror and electrode configuration controlling the plasma potential.

Extraction and beam characterisation. Once plasma performance is validated, a negative-ion extractor will be installed on the LAPLACE source. The extracted negative-ion beam from a single aperture will be characterised experimentally (beam current, divergence), providing a direct measurement of source performance relevant to ITER's accelerator requirements.

Feasibility study for integration at RFX. In parallel, and in close collaboration with Emanuele Sartori's team at Consorzio RFX, a feasibility study will assess the technical requirements and constraints for integrating the new source concept into the Neutral Beam Test Facility (NBTF) in Padova. This will combine engineering analysis of the RFX infrastructure with input from the plasma-physics results obtained at LAPLACE.

International mobility. The candidate will spend four months in total at RFX (Padova) over the course of the thesis, working directly with Sartori's team on extractor design, beam characterisation, and the integration feasibility study - ensuring that experimental and modelling work conducted at LAPLACE is continuously informed by injector-integration constraints from RFX, and vice versa.