Prediction of the likelihood of Alfvénic mode chirping in ITER baseline scenarios*

The confinement of fast ions is a critical issue to ensure ITER's burning plasma operation. ITER will employ two negative-ion-based neutral beam injection (NBI) sources, which will account for 33MW of injected power. Both the 3.5MeV fusion-born alpha particles and the tangentially injected 1MeV NBI ions will have supra-Alfvénic velocities, allowing them to interact with TAEs via their main resonance. Therefore, to predict and model Alfvénic mode evolution and the nature of fast ion transport due to Alfvénic instabilities in ITER, it is instructive to anticipate whether the modes will be more prone to have their frequencies locked to the background equilibrium or be subject to rapid chirps. Those two typical scenarios lead to mostly diffusive and convective losses, respectively. We present predictive studies of the probable spectral behavior of Alfvénic eigenmodes for baseline ITER cases consisting of elmy, advanced and hybrid scenarios. It has been observed that most cases are found to be in the borderline between the fixed-frequency steady and the chirping phases, with a tendency for steady response if additional stochasticity mechanisms, such as scattering due to radio frequency fields or mode overlap are present.