Tokamak plasmas are strongly nonlinear systems far from thermodynamic equilibrium, in which instabilities of very different spatial scales coexist, ranging from large-scale macroscopic oscillations to microturbulence. The presence of energetic ions produced by fusion reactions or by auxiliary heating further enhances these instabilities through wave–particle resonances. Microturbulence is responsible for heat and particle transport in the thermal plasma, while instabilities driven by energetic particles can induce their radial transport and, consequently, their losses. Both phenomena degrade the performance of present tokamak plasmas, and possibly also those of burning plasmas such as ITER.
Recent results, however, show that these instabilities, which have long been studied separately, can interact nonlinearly, and that this interaction may lead to an unexpected improvement of plasma confinement.
The objective of this project is to investigate these multiscale interactions using the gyrokinetic code GTC, which is able to simultaneously simulate turbulence and energetic-particle-driven instabilities. This work aims to improve the understanding of the nonlinear mechanisms governing plasma confinement and to identify optimal regimes for future fusion plasmas.

ITER and future fusion powerplants will need to operate without degrading too much the plasma facing components (PFC) in the divertor, the peripheral element with is dedicated to heat and particle exhaust in tokamaks. In this context, two key factors must be considered: heat fluxes must stay below engineering limits both in stationary conditions and during violent transient events. An operational regime recently developed can satisfy those two constraints: the X-point Radiator (XPR). Experiments on many tokamaks, in particular WEST which has the record plasma duration in this regime (> 40 seconds), have shown that it allowed to drastically reduce heat fluxes on PFCs by converting most of the plasma energy into photons and neutral particles, and that it also was able to mitigate – or even suppress – deleterious magnetohydrodynamic (MHD) edge instabilities known as ELMs (edge localised modes). The mechanisms governing these mitigation and suppression are still poorly understood. Additionally, the XPR itself can become unstable and trigger a disruption, i.e., a sudden loss of plasma confinement cause by global MHD instabilities.
The objectives of this PhD are: (i) understand the physics at play during the interaction XPR-ELMs, and (ii) optimise the access and stability of the XPR regime. To do so, the student will use the 3D non linear MHD code JOREK, the European reference code in the field. The goal is to define the operational limits of a stable XPR with small or no ELMs, and identify the main actuators (quantity and species of injected impurities, plasma geometry).
A participation to experimental campaigns of the WEST tokamak (operated by IRFM at CEA Cadarache) – and of the MAST-U tokamak operated by UKAEA – is also envisaged to confront numerical results and predictions to experimental measurements.