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Description
We report Doppler backscattering (DBS) measurements and gyrokinetic simulations of alternating Alfvénic bursts in a JET plasma previously analysed by Ruiz Ruiz et al. [Phys. Rev. Lett. 134, 095103 (2025)]. The DBS measurements show that fluctuation power in the ITG-turbulence frequency range is anticorrelated with the fluctuation power of modes in the gaps of the Alfvénic spectrum, with the ITG-range fluctuation power decreasing by nearly an order of magnitude during the Alfvénic bursts. The simultaneous growth of the fundamental TAE, higher-frequency sidebands, and ITG turbulence suppression indicates that the dynamics cannot be described by a simple delayed predator-prey cycle alone. The second sideband grows at approximately twice the rate of the fundamental TAE, consistent with beat-driven generation. Linear gyrokinetic stability analysis with CGYRO shows that the low-wavenumber EP-driven mode is localized near TAE half-rational surfaces, where neighbouring poloidal harmonics overlap. Nonlinear gyrokinetic simulations reproduce alternating Alfvénic bursts on timescales comparable to the DBS observations and show nonlinear generation of zonal fields and structures. Although zonal flows are generated near the half-rational surfaces of the fundamental TAE, their shearing rate remains below the ITG linear growth rate, suggesting that additional mechanisms contribute to the observed turbulence suppression. The simulations also show flattening of the energetic-particle gradient and of the thermal density and temperature gradients near the half-rational surfaces of the dominant TAE modes. These results suggest that zonal density and temperature structures contribute to TAE saturation and to the associated stabilization of ITG turbulence.