Alfvenic instabilities driven by alpha particles in ITER scenarios

Abstract. The stability of proposed ITER scenarios with respect to Alfvénic instabilities driven by fusion-produced alpha particles is investigated by hybrid MHD-particle simulations. Three cases are considered: the monotonic safety-factor scenario (SC2), the reversed-shear one (SC4) and a flat safety-factor profile “hybrid ” sce-nario (SCH). Though all the cases are found unstable, growth rates are quite small. The effects of nonlinear mode dynamics on the alpha-particle confinement at the reference drive are negligible for the SC2 and the SCH cases. For the SC4 scenario, some broadening of the alpha-particle pressure profile is observed, indicating inconsistency problems of the scenario itself. Such problems could arise for the other scenarios as well in the presence of a stronger drive (e.g., because of a moderate increase in electron and bulk-ion temperatures, or the inclusion of en-ergetic particles produced by additional heating methods). The SCH scenario, however, does not present relevant profile broadening, unless the threshold for Energetic Particle Mode (EPM) destabilization (a factor ∼ 1.6 greater than the reference pressure gradient) is exceeded. 1.