Multi-scale Interaction for Edge-Localized-Mode Suppression in Turbulent Pedestal in DIII-D plasmas*

The multi-scale pedestal turbulence interaction shows a viable means for suppression of Edge Localized Modes (ELMs). Specifically, how interactions between large-scale MHD and small-scale drift wave turbulence modulate particle flux is studied in DIII-D wide pedestal quiescent H-mode (WPQH). The large-scale, low-frequency MHD (10-60 kHz) rotates in the ion-diamagnetic direction and is identified as weakly excited Peeling-Ballooning (PB) mode; the small-scale, high-frequency turbulence (60kHz-2MHz) rotates in the electron-diamagnetic direction and is comprised of electron drift waves. Alternating evolution of PB mode fluctuations, electron drift waves, and background density/temperature gradients are observed in WPQH mode pedestals. BES velocimetry analysis reveals that strong bicoherence, negative inward turbulent particle flux, and scatter of the cross phase between density and radial velocity perturbation of MHD during an electron drift wave burst. Such results demonstrate that the interplay between scale-separated modes plays a crucial role in determining ELM dynamics. Synergistic numerical modeling demonstrates that small-scale electron drift waves scatter the cross phase of the pressure and radial velocity perturbation of PB mode, resulting in decoherence of the PB-driven flux. This scattering interaction prevents PB growth and suppresses the ELM. A theoretical model to quantify the impact of electron drift wave scattering on PB modes has also been developed. This work yields a novel nonlinear prediction of the shift of the ELM onset boundary induced by the ambient electron drift waves, thereby indicating when a turbulent pedestal can be maintained in a quiescent state in this scenario. In addition, this work showcases a new type of multi-scale interaction physics, which can play a role in a wide range of physical systems.