New High-Confinement Regime with Fast Ions in the Core of Fusion Plasmas

The key result of the present work is the theoretical prediction and observation of the formation of a new type of transport barrier in fusion plasmas, called F-ATB (fast ion-induced anomalous transport barrier). As demonstrated through state-of-the-art global electrostatic and electromagnetic simulations, the F-ATB is characterized by a full suppression of the turbulent transport-caused by strongly sheared, axisymmetric E x B flows-and an increase of the neoclassical counterpart, albeit keeping the overall fluxes at significantly reduced levels. The trigger mechanism is shown to be a mainly electrostatic resonant interaction between suprathermal particles, generated via ion-cyclotron-resonance heating, and plasma microturbulcncc. These findings are obtained by realistic simulations of the ASDEX Upgrade discharge No. 36637-properly designed to maximized the beneficial role of the wave-particle resonance interaction-which exhibits the expected properties of improved confinement produced by energetic particles.

Automated summary

The study predicts and observes the formation of a new type of transport barrier, F-ATB, in fusion plasmas. This barrier suppresses turbulent transport and increases the neoclassical counterpart while keeping overall fluxes at significantly reduced levels, achieved through realistic simulations of an ASDEX Upgrade discharge.