« Physique et Sciences de la Matière» : spécialité « Energie, Rayonnement et Plasma»
Soutiendra publiquement ses travaux de thèse intitulés :
« Interaction between runaway electrons and cold plasmas: application to disruption mitigation in tokamaks »
dirigés par Dr. Peter Beyer et Cédric REUX
Soutenance prévue le jeudi 11 septembre 2025 à 14h30 en salle René Gravier
Composition du jury :
| Dr. Alberto LOARTE | ITER | Rapporteur |
| Dr. Gabriella PAUTASSO | IPP, Garching | Rapporteur |
| Dr. Pascale HENNEQUIN | LPP, Palaiseau | Présidente du jury |
| Dr. Jérôme BUCALOSSI | IRFM, CEA, Cadarache | Examinateur |
| Dr. Joan DECKER | SPC, EPFL, Lausanne | Examinateur |
| Dr. Istvan PUZTAI | Chalmers, Göteborg | Examinateur |
| Dr. Peter BEYER | PIIM, Aix-Marseille Université | Directeur de thèse |
| Dr. Cédric REUX | IRFM, CEA, Cadarache | Co-directeur de thèse |
Keywords:
Tokamak plasmas, Runaway electrons, Background plasma, Disruption, Bolometers
Abstract:
Disruptions in tokamak plasmas remain a major challenge in achieving energy generation with a fusion power plant. The abrupt release of the plasma’s stored thermal and magnetic energy can lead to severe consequences, including intense heat loads, large electromagnetic forces, and the generation of highly energetic electrons called runaway electrons (REs). These REs can carry a substantial fraction of the plasma current and, upon impact with the wall, cause severe damage and even melting of plasma-facing components. As tokamaks, such as ITER, approach fusion power plant conditions with increasingly high plasma currents, their complete suppression during disruptions cannot be guaranteed. If avoidance proves impossible, massive low-Z injections (deuterium, hydrogen) have been shown to be effective at mitigating RE beams with currents of the order of the megaampere, with no damage or significant heat loads, a benign termination. The benign termination scheme shows promise, but a detailed understanding of its mechanisms is essential to assess its applicability to RE beams in ITER and future tokamaks.
In this thesis, we explore the operational limits of the benign termination in the JET tokamak. Notably, the partial recombination of the companion plasma, the cold plasma coexisting with the REs, is essential for a successful benign termination. This recombination is dictated by the power balance between heating from RE collisions and energy loss mechanisms: mainly conductive and radiative power losses from the additional low-Z atoms. The recombination conditions determine, in part, the operational limits of the benign termination in the quantity of low-Z material, the quantity of impurities used to trigger the disruption and the RE density. The power lost through radiation is measured by resistive bolometers and is essential to evaluate the power balance of the companion plasma. However, we show that the bolometers used to measure the total radiated power loss can be significantly affected by the massive material injections and induce a spurious signal reaching several megawatts of radiated power. Finally, we take the first steps at modelling self-consistently the companion plasma and its interactions with runaway electrons using the code DREAM to investigate the recombination conditions of the companion plasma
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