Understanding the transport and losses of energetic particles in Tokamaks is crucial for operating future fusion reactors. Indeed, energetic particles can resonate with eigenmodes of the thermal plasma and, via this interaction, be expelled before being able to deposit their energy in the Tokamak core, and maintaining their proper high-temperature conditions for having Fusion reactions.
In particular, trapped energetic particles resonate with the low-frequency kink mode, leading to a growing ''Fishbone'' instability. These particles can be generated by heating systems in D-D experiments, or can correspond to the population of Alpha particles with a velocity mainly perpendicular to the ambient magnetic field, in D-T experiments.

The future researcher will investigate the dynamics of the Fishbone instability, and that of particles, with the aid of two different numerical codes, and experimental data from the D-T campaign of JET. The two codes are complementary. The first one (BAK-RM) adopts a simplified model, where the thermal plasma is described using reduced MHD, coupled to the dynamics of deeply trapped energetic particles only, described by a gyro- and bounce-averaged Vlasov equation. This code is developed at the PIIM laboratory and has the great advantage of selecting only part of the complex physics determining the Fishbone dynamics, in a simplified geometry. The second code (XTOR-K), developed by H. Lütjens at the CPHT laboratory (Palaiseau), provides a more complete description where full MHD equations describe the thermal plasma while trapped and passing energetic particles are treated kinetically in the full 3D3V phase-space.
The numerical results will be compared to the experimental data of the recent D-T campaign of JET, in collaboration with R. Dumont (IRFM, CEA Cadarache).

The combined action of a reduced model, a more realistic one and experimental measurements, have the aim of understanding the mode dynamics, in particular during its nonlinear phase, and its impact on energetic particle radial transport.

Keywords : Plasma Physics, Magnetically Confinment Fusion, Numerical simulations, Energetic particles in Tokamaks