Interaction Between Energetic Particle Driven Instabilities And Microturbulence In Tokamak Plasmas H/F CEA

Tokamak plasmas are nonlinear systems far from thermodynamic equilibrium, characterized by a broad range of interacting instabilities that span from macroscopic oscillations, comparable to the device size, down to microturbulent fluctuations smaller than the ion Larmor radius. These instabilities arise from the large free energy stored in plasma gradients typical of the tokamak configuration.The presence of energetic ions, produced either by fusion reactions or auxiliary heating systems, adds further complexity. Such particles can resonate with plasma waves, exciting kinetic instabilities on meso- to macro-scales and enhancing cross-scale couplings. Both microturbulence and energetic particle (EP)-driven instabilities negatively affect plasma performance: the former drives anomalous transport of heat and particles, while the latter can induce radial redistribution or losses of EPs, limiting their contribution to plasma heating.
Traditionally, these processes have been studied separately, assuming that their characteristic scales were too distant to interact. However, recent experiments and simulations have shown that these scales can couple through zonal flows, i.e. axisymmetric perturbations of the electrostatic potential that regulate turbulence. In some cases, EP-driven instabilities can even amplify zonal flows, unexpectedly reducing turbulence and improving confinement. Understanding these nonlinear mechanisms is crucial for optimizing performance in future fusion reactors.
This project aims to explore the interaction between EP-driven instabilities and microturbulence using the Gyrokinetic Toroidal Code (GTC), a global particle-in-cell (PIC) code well suited for studying multi-scale phenomena in realistic tokamak geometries.
The work will proceed in two main stages. In the first, the student will contribute to extending GTC to handle multiple energetic particle species, instead of a single one. This development will provide both experience with the code structure and insight into the physics of isolated ITG turbulence and EP-driven Alfvénic modes. It will also enable more realistic modeling of burning plasmas, such as those expected in ITER, where multiple EP species coexist.
In the second stage, nonlinear simulations including both EP-driven instabilities and microturbulence will be carried out for selected JET discharges, where enhanced confinement has been experimentally observed. These studies will allow a systematic investigation of cross-scale couplings and their role in transport regulation.
While ambitious for a six-month internship, this project lays the foundation for a Ph.D. within the ANR JCJC SFIT project, focusing on nonlinear multi-scale plasma dynamics. The ultimate goal is to deepen the understanding of the interplay between energetic particle physics and microturbulence, and to identify operational regimes that optimize plasma confinement in future fusion devices such as ITER.