Global gyrokinetic simulations of Alfvén modes in ITER plasmas.

The global gyrokinetic code ORB5 [S. Jolliet et al., Comp. Phys. Comm., 177, 409 (2007)] can simultaneously include electromagnetic perturbations, shaped MHD axisymmetric equilibria, zonal-flow preserving sources, collisions, and the ability to solve the full core plasma including the magnetic axis. Multiple ion species are described by gyrokinetic equations, while a drift-kinetic model is generally used for the electrons. Recently, the algorithm of the electromagnetic solver has been rewritten, based on the so-called mixed-variable formulation of the gyrokinetic theory [A. Mishchenko et al., Phys. Plasmas 21, 052113 (2014)]. The resulting code allows for significantly larger time steps even for experimentally relevant conditions. It has been applied to different Alfénic physics problems and verified against other existing codes. In this work, we focus on the role of Alfvén instabilities, driven unstable by an energetic particle population, in the standard ITER 15MA scenario (high-beta equilibrium) with realistic density and temperature profiles for thermal ions, electrons and energetic particles. The results obtained by those costly global simulations are particularly valuable for the validation of simpler analytical or hybrid-kinetic models.