Directeur de these    M. Eric SERRE CNRS M2P2

Rapporteur            M. Benjamin DUDSON Lawrence Livermore National Laboratory

Rapporteur            M. Boniface NKONGA Université Côté d'Azur

Examinateur            M. Paolo RICCI EPFL

Président            M. Eric NARDON CEA Cadarache

Examinateur            Mme Daniela GRASSO Politecnico de Torino

Co-encadrant de these M. Hugo BUFFERAND CEA Cadarache

Date : jeudi 12/12 à 14h00, amphi N°3 ; Centrale Méditerranée ; 38 rue Joliot-Curie, 13013 Marseille

Abstract : To control heat deposition on the Plasma-Facing Components (PFCs) of current tokamaks and future reactors, a major effort is underway to develop fluid codes that can model turbulent transport in the plasma edge. Understanding the underlying physical processes is one of the key challenges in magnetic fusion research, especially with the upcoming launch of the International Thermonuclear Experimental Reactor (ITER). Despite significant advances in plasma fluid simulations, several challenges in the modelling remain. These include limitations related to fixed magnetic equilibrium, simplified boundary conditions to model plasma wall interactions, time-consuming neutral transport simulations, crude perpendicular turbulent transport models, and limited coupling between the plasma core and the Scrape-Off Layer (SOL). These limitations hinder full-discharge simulations, restricting analysis to a few snapshots of relatively stable plasma phases, which still carry significant uncertainties. This thesis contributes to the ongoing development of the SolEdge-Hybridized Discontinuous Galerkin (HDG) code, a magnetic equilibrium-free fluid plasma solver. The research focuses on improving the physical completeness of the code and enhancing its ability for experimental validation. A detailed overview of the SolEdge-HDG code is provided, highlighting the initial models and assumptions. The implementation of the HDG method is discussed, which allows the use of high-order meshes that are not aligned with the magnetic field, enabling precise descriptions of tokamak wall geometries. Key developments in the SolEdge-HDG suite include the creation of synthetic diagnostics (bolometer and visible range cameras), improving the code's ability to compare simulations with experimental data. These comparisons revealed shortcomings in the initial physical models, which have been addressed in this thesis. Improvements include a more consistent neutral fluid model, which is crucial for understanding tokamak fueling, as well as the introduction of new heat sources and a self-consistent heuristic perpendicular turbulent transport fluid model. The enhanced SolEdge-HDG code successfully captures key plasma regimes, such as sheath-limited, high-recycling, and detached states. A detailed study is conducted on the plasma’s response to variations in gas puffing, demonstrating its impact on tungsten sputtering. The extension of the bolometer system in WEST for more accurate measurements is also explored, as well as potential applications of visible camera diagnostics. The thesis demonstrates the first application of the self-consistent turbulent model to simulate a full cross-section during the ramp-up phase of a WEST discharge. The simulation results show qualitative agreement with experimental data. The interaction between evolving plasma equilibrium and the turbulent model is also discussed, with emphasis on its effect on divertor heat load predictions. Applications of the fully upgraded SolEdge-HDG model are further explored for steady-state plasmas with additional heating. Special attention is given to the turbulent model’s response to different heating methods and the process of ion-electron energy equilibration. Finally, the thesis illustrates the application of SolEdge-HDG and synthetic diagnostics to improve tokamak design. It examines the impact of reflections on bolometer signals and evaluates various approaches for tomographic inversions of plasma radiation. An application to the final design of the ITER bolometer system is also presented. This work demonstrates the expanded capabilities given by magnetic-equilibrium-free solver for tokamak design and operation. The integration of synthetic diagnostics not only allows to confront simulations to the experiments, but also sheds light to the model’s weaknesses. While some limitations remain, the code suite is already capable to solve key operational design challenges. 

Directeur de these          M. Eric SERRE CNRS, M2P2

Co-encadrant de these  Mme Anna GLASSER CNRS, M2P2

Président                  Mme Pascale HENNEQUIN CNRS, LPP

Examinateur                  M. Alberto LOARTE ITER

Rapporteur                  Mme Eleonora VIEZZER University of Sevilla

Rapporteur                  M. Jeremy LORE ORNL

Abstract : Phosphorus (P) is an essential nutrient for global food production, but intensive agriculture disrupts its natural cycle, increasing reliance on non-renewable sources. A sustainable alternative is recovering P from renewable organic waste streams such as sewage sludge and digestate. This PhD thesis investigates the hydrothermal treatment of sewage sludge to explore P conversion and speciation, aiming to valorize the mineral phase as fertilizer and the organic phase as bio-oil. Two types of sludge, differing in solids content and composition, were sampled from a wastewater treatment plant in southern France. The sludge was treated in a batch reactor at temperatures varying from 250 to 350 °C for 5 to 45 min. Products were centrifuged into a solid pellet and process water, followed by characterization of their physicochemical properties. Results show that temperature and treatment duration significantly impact by-product characteristics, including their P content and speciation. Higher temperatures and longer times improve bio-oil yield. Treatments at 250-300 °C promote organic P mineralization and increase soluble phosphate concentration in the process water, while treatments at 350 °C lead to greater P recovery yield in the solid pellet (> 90%). Higher calcium and iron contents of sludge improve orthophosphate precipitation, and calcium oxide addition enhances P recovery in the solid pellet as calcium phosphate. This research provides a framework for sustainable P recovery, suggesting hydrothermally treated pellets as potential slow[1]release fertilizers. Future work should include detailed bio-oil characterization to better assess the energy recovery potential.

Keywords : residual biomass, phosphorus recovery, hydrothermal liquefaction, sewage sludge, circular economy.

Benedetta DE CAPRARIIS,       Reviewer, Associate professor, La Sapienza University of Rome

Véronique DELUCHAT,             Reviewer, Professor, Limoges University

Anthony DUFOUR,                   Examiner, Senior scientist, CNRS LRGP

Jean-Henry FERRASSE,           Examiner, Professor, Aix-Marseille University

Mathieu GAUTIER,                   Examiner, Professor, INSA Lyon

Elsa WEISS-HORTALA,            Examiner, Assistant professor, IMT Mines Albi

Olivier BOUTIN,                       Thesis supervisor, Professor, Aix-Marseille University

Cristian BARCA,                       Thesis co-supervisor, Associate professor, Aix-Marseille University