Description du sujet de thèse

The plasma theory team at CPHT is actively involved in fusion plasma research, which is of vital importance for several reasons: nuclear fusion offers a virtually unlimited, clean, and safe energy source. The fuel for nuclear fusion is abundant and easy to obtain. Moreover, nuclear fusion does not produce greenhouse gases or long-lived radioactive waste.
Mastering nuclear fusion represents an immense scientific and technological challenge. Recent progress is promising and supported by the development of large-scale facilities designed to confine the plasma using intense magnetic fields (tokamaks and stellarators).
The plasma theory team at CPHT specializes in developing models and numerical simulation tools, relying on simplified models to reduce computational time and facilitate result analysis, and on more sophisticated simulation codes to account for the complex physical phenomena occurring in plasmas. The plasma theory team is proposing a PhD project focused on optimizing stellarator design.
Until now, tokamaks, such as the experimental ITER reactor, have been leading the race in magnetic confinement fusion research, but in recent years, another type of toroidal magnetic confinement device, the stellarator, has emerged as a credible alternative. Invented in the 1950s like the tokamak, the stellarator has the advantage of not requiring the millions of amperes of current that circulate in tokamak plasmas. On the other hand, the electromagnetic coil structures are extremely complex and generally not confined to a single plane. Designing a stellarator first requires optimizing the three-dimensional topology of the magnetic field with respect to a number of physical and mechanical objectives, and then computing a set of electromagnetic coils that generate this configuration, taking into account the field perturbations caused by plasma pressure. Since plasma pressure—and therefore nuclear reactivity—is limited by magnetic pressure, high-temperature superconductors (HTS) open the possibility for more compact machines. However, a machine with higher power density and stronger magnetic fields faces mechanical and thermal challenges related to the confinement vessel. The goal of the PhD is to identify a minimum size for a high-field stellarator, considering these constraints.
The PhD will take place in several phases:
A bibliographic phase to become familiar with stellarator-specific concepts and optimization targets, as well as to acquire simulation tools for 3D equilibrium (e.g., the VMEC code) and coil design (e.g., the REGCOIL code).
Development of a stellarator optimization code based on these numerical tools. The code should focus on satisfying the most critical constraints related to stellarator size: neutron shielding, heat exhaust, and mechanical stresses on the coils.
Determination of a minimum size for a given configuration type, as a function of magnetic field strength.
Today, the very large size of stellarators is one of the major obstacles to their viability as reactors. The size (and cost) reduction enabled by HTS is not yet well understood, and this PhD will contribute to clarifying this crucial issue for the development of controlled thermonuclear fusion.

Contexte de travail

The PhD will take place within the plasma theory team at the Centre de Physique Théorique of École Polytechnique. Daily supervision is provided, as the PhD student will be based in the same laboratory as the advisors. Weekly meetings are organized, but the student is encouraged to meet with the advisors as often as needed. The work is closely guided during the initial (bibliographic and exploratory) phase and gradually left more to the student's initiative as the research progresses. In addition, the group currently supervises other PhD students, with whom scientific interactions are expected to develop. Finally, a thesis advisory committee meets annually.

Le poste se situe dans un secteur relevant de la protection du potentiel scientifique et technique (PPST), et nécessite donc, conformément à la réglementation, que votre arrivée soit autorisée par l'autorité compétente du MESR.