Observation of fast-ion driven Alfvén-eigenmodes in JET and their effect on turbulence and thermal transport.

Recent experiments using the 3-ion ICRH heating scheme [Kazakov NF 2015] have been successful at generating substantial populations of MeV range fast ions in the deep core of JET, mimicking the effect of fusion-born alpha particles in future burning plasmas. These fast ions are capable of destabilizing a wide range of Alfvén modes as observed using magnetics, reflectometer and Doppler backscattering measurements. Previous nonlinear gyrokinetic simulations have shown that turbulence existing at the ion-gyroradius scale can be stabilized [Mazzi Nat. Phys. 2022, PPCF 2022], producing close to neoclassical levels of ion heat flux. This results in a thermal transport regime dominated by the electron heat flux. We report on the transport and gyrokinetic modelling using GS2 in conditions when Alfvén eigenmodes are both stable and unstable, as observed from magnetics and Doppler backscattering fluctuation measurements. We probe the origins of the anomalous electron thermal transport in the presence of MeV range fast ions and unstable Alfvén eigenmodes. The implications of these scenarios to burning plasmas will be discussed.