Numerical validation of the electromagnetic gyrokinetic code NEMORB on global axisymmetric modes

In this paper, we report on a comparison of collisionless simulations on global modes (i.e. low poloidal mode number) with the gyrokinetic particle-in-cell code NEMORB against analytical theory and the gyrokinetic semilagrangian code GYSELA. Only axisymmetric modes, i.e. with toroidal mode number n = 0, are considered, and flat equilibrium profiles. Benchmarks are performed for geodesic acoustic modes against local analytical theory. In the presence of energetic ions, benchmarks of NEMORB are performed against GYSELA. The models of adiabatic versus trapped-kinetic versus fully kinetic-electrons and of electrostatic versus electromagnetic at very low beta are compared. Scalings of Alfven modes are also presented.