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. We analyze an ICRH heated L-mode in which fast ions destabilized a wide range of Alfvén eigenmodes (AEs) as observed using magnetics, reflectometer and Doppler backscattering (DBS) measurements. As ICRH heating power was increased and AEs were destabilized (DBS), we observed an increase in the electron thermal transport (dominant to the ion thermal transport inside rho = 0.4) and an increase in the deep core ion temperature. This is consistent with previous nonlinear turbulence simulations suggesting that AEs can stabilize ion-scale turbulence [DiSiena NF 2019, Mazzi Nat. Phys. 2022], however electron thermal transport remains a mystery. We report on the transport and gyrokinetic modelling using GS2 and CGYRO in conditions when Alfvén eigenmodes are both stable and unstable, as observed from magnetics and DBS 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.