The confinement of energetic particles (EP) is crucial for an efficient
heating of tokamak plasmas. Plasma instabilities such as Alfven Eigenmodes (AE)
can redistribute the EP population making the plasma heating less effective,
and leading to additional loads on the walls. The nonlinear dynamics of
toroidicity induced AE (TAE) is investigated by means of the global gyrokinetic
particle-in-cell code ORB5, within the NEMORB project. The nonperturbative
nonlinear interplay of TAEs and EP due to the wave-particle nonlinearity is
studied. In particular, we focus on the nonlinear modification of the
frequency, growth rate and radial structure of the TAE, depending on the
evolution of the EP distribution in phase space. For the ITPA benchmark case,
we find that the frequency increases when the growth rate decreases, and the
mode shrinks radially. This nonlinear evolution is found to be correctly
reproduced by means of a quasilinear model, namely a model where the linear
effects of the nonlinearly modified EP distribution function are retained.Comment: Submitted to Plasma Phys. Control. Fusio
