The suppression of the microturbulence associated to the emergence of a spontaneous internal transport barrier has been recently demonstrated in a system showing a possible amplification of the zonal flow component in the low-frequency regime (Ghizzo and Del Sarto 2023 Nucl. Fusion63 104002). We use here numerical experiments performed with a 'particles modes' model based on a double average over the fast cyclotron phase and over the bounce (or transit) phase to show the major role played by energetic particles and shear flows in this scenario. 'Particle modes' are meant here as classes of particles, identified by some adiabatic invariant after a gyro-average procedure, which are associated to the description of some specific linear modes of the plasma. The introduction of energetic circulating ions or shear flows into the system makes a larger number of particle modes being involved in the synchronization process. A global synchronization of the Fourier modes of the turbulent spectrum can be this way achieved. This process allows for a bifurcation towards self-organization, which is associated to the emergence of a staircase-like structure. This is known to be an essential element in the modification of the zonal flow pattern in phase space during the suppression of microturbulence in tokamaks.
This paper explores how the suppression of microturbulence and the emergence of a spontaneous internal transport barrier are linked to the synchronization of zonal flows with energetic particle modes. Numerical experiments show that the introduction of energetic circulating ions or shear flows can lead to a global synchronization of the turbulent spectrum, allowing for a bifurcation towards self-organization and the formation of a staircase-like structure, which is essential for modifying the zonal flow pattern and suppressing microturbulence in tokamaks.